This work was supported by the School of Chemical Engineering, Purdue University. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. MRCAT operations, beamline 10-BM are supported by the Department of Energy and the MRCAT member institutions. The authors also acknowledge the use of beamline 11-ID-C. We thank Evan Wegener for experimental assistance with the XAS.

1. Synthesis of Supported 2 nm Pt-Cu Bimetallic Nanoparticle Catalysts
<ol>
	<li>Preparation of metal precursor solution
	<ol>
		<li>Dissolve 0.125 g of copper nitrate trihydrate (Cu(NO3)2&#183;3H2O) in 1 mL of water to achieve a sky blue solution. 
		Caution: Use protective gloves when handling chemicals.</li>
		<li>Add ammonia dropwise to the copper nitrate solution, forming dark blue precipitates of copper hydroxide. 
		Caution: Use a fume hood for handling bases and volatile chemicals.</li>
		<li>Keep adding ammonia until the dark blue precipitates dissolve to form a dark blue solution and the pH&#160;&#62;10.</li>
		<li>Add 0.198 g of tetraammineplatinum nitrate ((NH3)4Pt(NO3)2) to the solution and additional water so that the total volume of the solution is 3.5 mL. Add additional ammonia if necessary to keep the pH of the solution greater than 10.</li>
		<li>Heat the solution to 70 &#176;C until all the tetraammineplatinum nitrate salts are dissolved in the solution. Allow the solution cool to RT.</li>
	</ol>
	</li>
	<li>Co-impregnation of metal precursor solution
	<ol>
		<li>Prior to catalyst preparation, determine the impregnating pore volume of the silica support. Carefully weigh approximately 5 g of dry silica into a weighting dish. While mixing, add H2O dropwise until the silica is completely wet, but with no excess solution. Reweigh the wet silica. Divide the grams of added water by the grams of sample to calculate the pore volume.</li>
		<li>Add the dissolved metal precursor solution a few drops at a time to 5 g of high-porous silica (SiO2) in a ceramic evaporating dish and stir gently to break up the particles that stick together to achieve a homogeneous distribution of the solution. 
		NOTE: The white silica will turn dark blue once it adsorbs all 3.5 mL of metal precursor solution.
		<ol>
			<li>Make sure that the texture of the silica particles remains like that of dry sand. Avoid the accumulation of excess solution during impregnation.</li>
		</ol>
		</li>
		<li>Place the impregnated Pt-0.7Cu/SiO2 catalyst precursor into a drying oven and dry it at 125 &#176;C O/N.</li>
	</ol>
	</li>
	<li>Calcination and reduction
	<ol>
		<li>Calcine the catalyst in a furnace at 250 &#176;C with a 5 &#176;C/min ramp rate in air for 3 h. 
		NOTE: Calcination at higher temperatures generally leads to larger Pt nanoparticles.</li>
		<li>Place a 2 cm layer of quartz wool in the middle of a 1&#34; quartz tube reactor and load the calcined Pt-0.7Cu/SiO2 catalyst into the tube through a plastic funnel. Place the tube in a clamshell temperature-programmed furnace.</li>
		<li>After purging the tube with N2 for 5 min at RT, start to flow H2 (at RT) at the same flow rate as N2 (100 ccm) to reduce the Pt-0.7Cu/SiO2 catalyst.</li>
		<li>Increase the temperature to 150 &#176;C with a 5 &#176;C/min ramp rate and hold for 5 min.</li>
		<li>Start slow ramping the temperature at a rate of 2.5 &#176;C/min to 250 &#176;C. Hold the temperature for 15 min at every 25 &#176;C. 
		NOTE: Other metals may require lower or higher temperatures of reduction. The exact temperature can generally be determined by examining color changes of the catalyst (e.g., from blue to black) for Pt-Cu.</li>
		<li>Ramp to 550 &#176;C (or the reaction temperature, if higher) at 10 &#176;C/min and stay for 30 min to complete the reduction. Purge with N2 and cool to room temperature.</li>
		<li>Unload the Pt-0.7Cu/SiO2 catalysts and store in a vial for future use. 
		NOTE: Repeat similar synthesis procedures using different amount of Cu(NO3)2&#183;3H2O and (NH3)4Pt(NO3)2 to prepare the other Pt-X Cu/SiO2 catalysts (X = 0.7, 2.3, and 7.3 and stands for Cu:Pt atomic ratios) and Pt/SiO2 catalysts.</li>
	</ol>
	</li>
</ol>
2. Propane-dehydrogenation Performance Test
<ol>
	<li>Catalyst loading
	<ol>
		<li>Take a 3/8&#34; quartz tube reactor and place a 1 cm layer of quartz wool against the dimple in the middle. 
		Caution: Use protective gloves when handling quartz wool, since the fine needles can get imbedded in the skin.</li>
		<li>Weigh 40 mg of Pt-0.7Cu/SiO2 catalyst and 960 mg of the silica for dilution. Mix the particles (1 g total weight) in an empty vial.</li>
		<li>Use a plastic funnel to load all the catalyst mixture into the reaction tube. Wipe the outer wall of both tube ends with lint-free wipes to remove any dirt to get a good seal with the O-ring.</li>
		<li>Put the tube fittings onto both ends of the quartz reactor tube and attach them to the reactor system equipped with a clamshell furnace.</li>
	</ol>
	</li>
	<li>Leak test and catalyst pretreatment
	<ol>
		<li>Turn on 50 cm3/min N2 flow through the tube reactor. After 1 min, close the ball valve on the reactor outlet. Wait for the system pressure to increase to 5 psig. Close the ball valve on the inlet N2 line to stop N2 flow and seal the reactor system.</li>
		<li>Wait for 1 min and record the pressure read from the gauge. If the pressure drops, open the ball valve on the reactor outlet to release the pressure and re-attach the fittings. If not, first open the ball valve on the reactor outlet to release the pressure before restarting the N2 flow by turning on the ball valve on the inlet N2 line to purge the system for 1 min.</li>
		<li>Start flowing 50 cm3/min of 5% H2/N2 for catalyst reduction before running a reaction and stop the N2 flow. Start heating the tube to the reaction temperature of 550 &#176;C, with a rate of 10 &#176;C/min. Wait for 30 min after the furnace reaches the set point and allow the system temperature to stabilize at the target temperature.</li>
	</ol>
	</li>
	<li>Propane dehydrogenation reaction testing
	<ol>
		<li>Start the gas chromatograph (GC) in the reactor system and select the proper method for gas component analysis.
		<ol>
			<li>Switch the reactor gas flow to a bypass line. Flow 100 cm3/min of 5% propane/N2 and 100 cm3/min of 5% H2/N2. Wait for 1 min so that the propane flow stabilizes and inject the bypass flow into GC as a reference sample.</li>
		</ol>
		</li>
		<li>Switch the gas flow back to the reactor tube line to start the reaction and record the time.</li>
		<li>After the reaction runs for 4 min, inject the reactor outlet gas flow (a GC sample) into the GC to get the outlet gas component information. Inject samples every 4 min and run the test until the conversion reaches steady state or the conversion is very low.</li>
		<li>Use the corresponding peak analysis software to analyze each peak.
		<ol>
			<li>Click to select the start and end points of the peak. Use the integrate function to get the peak area. Write down the peak area for the propane (C3H8) reactant; the propylene (C3H6) product; and the side products, methane (CH4), ethane (C2H4), and ethylene (C2H6). 
			NOTE: For each injection, a GC pattern with multiple peaks is obtained whose area relates to the number of moles of different gas species.</li>
		</ol>
		</li>
		<li>Convert the peak area to the number of moles for each species using the response factor. Determine the propane conversion and propylene selectivity at the time for each sample according to the following formulas: 
		<img alt="Equation" src="/files/ftp_upload/56040/56040eq1.jpg" /> 
		<img alt="Equation" src="/files/ftp_upload/56040/56040eq2.jpg" /> 
		where <img alt="Equation" src="/files/ftp_upload/56040/56040eq3.jpg" /> is the conversion of propane, <img alt="Equation" src="/files/ftp_upload/56040/56040eq4.jpg" /> is the propylene selectivity, <img alt="Equation" src="/files/ftp_upload/56040/56040eq5.jpg" /> is the number of moles of propane, and <img alt="Equation" src="/files/ftp_upload/56040/56040eq6.jpg" /> is the number of moles of propylene.</li>
		<li>Obtain the initial conversion and selectivity value at t = 0 by extrapolating the measured conversion and selectivity versus time on stream using an exponential fit.</li>
	</ol>
	</li>
	<li>Post-reaction
	<ol>
		<li>Stop heating the reactor by turning off the temperature program. Switch the gas flow to 10 cm3/min N2.</li>
		<li>Switch the gas chromatograph back to standby method to reduce the flow rate of the carrier gas.</li>
		<li>Unload the used catalyst from the quartz fix-bed reactor after cooling to room temperature. Collect the catalyst weight in a designated waste disposal area.</li>
	</ol>
	</li>
</ol>
3. Characterization of Catalyst Samples
<ol>
	<li>Scanning Transmission Electron Microscopy4,20
	<ol>
		<li>Load the catalyst in a mortar and grind it into less than 100 mesh powder using a pestle.</li>
		<li>Disperse about 30 mg of catalyst powder into about 5 mL of isopropyl alcohol in a small vial. Shake the vial for full mixing and then let the vial sit for 5 min to allow for the deposition of the relatively large particles. 
		NOTE: The obtained suspension should contain very small particles of supported catalysts.</li>
		<li>Place a Au TEM ready grid on an evaporating dish. Heat the dish to 80 &#176;C on a hot plate. Add three drops of the catalyst suspension to the grid. 
		NOTE: The isopropyl alcohol will evaporate quickly and leave the catalyst particles on the grid.</li>
		<li>Load the grid onto the sample holder for electron microscopy sample imaging.</li>
	</ol>
	</li>
	<li>In situ X-ray absorption spectroscopy3,4,19,20
	<ol>
		<li>Load the catalyst into a mortar and grind it into less than 100 mesh powder using a pestle. Load the fine powders into a die set and press it with the fingers to form a self-supporting wafer.</li>
		<li>Load a ~100 mg sample into the sample holder.</li>
		<li>Place the sample holder into a quartz tube reactor and pretreat the sample by reducing it in 50 cm3/min 3% H2/He.</li>
		<li>After cooling to RT, seal the tube and transfer it to the synchrotron beamline to collect the XAS data.</li>
	</ol>
	</li>
	<li>In situ X-ray diffraction 19,20
	<ol>
		<li>Load the catalyst in a mortar and grind it into less than 100 mesh powder using a pestle.</li>
		<li>Press a thin wafer using a standard 7 mm diameter die set. 
		NOTE: The die set contains a female piece and top and bottom male pieces.
		<ol>
			<li>Attach the bottom male piece to the female part. Load the sample onto the polished surface of the bottom part. Attach the top male piece and transfer the die set to the sample stage of the press. Press with appropriate strength.</li>
		</ol>
		</li>
		<li>Unload the wafer and transfer it to the ceramic cup of the specialized sample stage (see the Table of Materials). Seal the stage and fix it on the sample table on the beamline.</li>
		<li>Reduce the sample by flowing and ramping the temperature to 550 &#176;C. Collect the in situ X-ray diffraction data under 3% H2/He gas flow at 550 &#176;C and after cooling down to RT20.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The Pt-Cu catalysts prepared in this work contain uniform nanoparticles around 2 nm in size, similar to heterogeneous catalysts qualified for industrial application. All the Pt and Cu precursors form bimetallic structures, as opposed to separate monometallic particles. This bimetallic interaction and small particle size are realized by careful control over the synthesis procedures. The impregnation process makes use of the Strong Electrostatic Adsorption (SEA) between metal ions and the surface of certain oxide supports<...

Propane dehydrogenation (PDH) is a key processing step in the production of propylene, taking advantage of shale gas, the fastest growing source of gas in the country1. This reaction breaks two C-H bonds in a propane molecule to form one propylene and molecular hydrogen. Noble metal catalysts, including Pd nanoparticles, exhibit poor selectivity for PDH, breaking the C-C bond to produce methane with a high yield, with the concomitant production of coke, leading to catalyst deactivation. Recent reports showed that selective PDH catalysts could be obtained by the addition of promoters like Zn or In to Pd2,3,4. The promoted catalysts are near 100% selective to PDH, as opposed to less than 50% for monometallic Pd nanoparticles of the same size. The great improvement in selectivity was attributed to the formation of PdZn or PdIn intermetallic compound (IMC) structures on the catalyst surface. The ordered array of two different types of atoms in the IMCs geometrically isolated the Pd active sites with non-catalytic Zn or In atoms, which turned off the side reactions catalyzed by an ensemble (group) of neighboring Pd active sites.
Platinum has the highest intrinsic selectivity among noble metals for propane dehydrogenation, but it is still not satisfactory for commercial use1. Typically, Sn, Zn, In, or Ga is added as promoter for Pt5,6,7,8,9,10,11,12,13. Based on the idea that geometric active site isolation contributes to high selectivity, any non-catalytic element forming an alloy structure with Pt, such as Cu, should also potentially promote catalyst performance14. Several previous studies suggested that the addition of Cu indeed improved the PDH selectivity of Pt catalysts15,16,17,18. Nevertheless, no direct evidence has been reported to determine whether Pt and Cu form bimetallic nanoparticles or ordered structures, which is crucial to understanding the promotional effect of Cu. In the binary phase diagram of Pt-Cu, two different structure types are possible over a wide composition range16,18: intermetallic compound, in which Pt and Cu each occupy specific crystal sites, and solid solution, in which Cu randomly substitutes in the Pt lattice. IMCs form at low temperature and transform into solid solution at around 600 - 800 &#176;C for bulk materials14. This transformation temperature may be lower for nanoparticles, near the reaction temperature of PDH (i.e.&#160;550 &#176;C). Therefore, it is essential to investigate the atomic order of Pt-Cu under reaction conditions. For supported nanoparticles with small particle sizes, it is very challenging to obtain meaningful structural information using laboratory instruments19. The limited repetition of unit cells leads to very broad diffraction peaks with very low intensities. Because of the high fraction of surface atoms in nanoparticles 1 - 3 nm in size, which are oxidized in air, diffraction must be collected in situ using high-flux X-ray, typically available with synchrotron techniques.
The previously reported Pt-Cu PDH catalysts were all larger than 5 nm in size15,16,17,18. However, for noble metal nanoparticle catalysts, there is always a strong desire to maximize catalytic activity per unit cost by synthesizing catalysts with high dispersions (typically around or less than 2 nm in size)19. Though the preparation of bimetallic nanoparticles of this size is possible by standard impregnation methods, rational control over the procedures is necessary. The metal precursors, pH of the impregnating solution, and support type need to be controlled to optimize the anchoring of the metal species onto high-surface area supports. The subsequent calcination and reduction heat treatments should also be carefully controlled to suppress the growth of the metallic nanoparticles.
This article covers the protocol for the synthesis of supported 2 nm Pt-Cu bimetallic nanoparticle catalysts and for the testing of their propane dehydrogenation performance. The structure of the catalysts is investigated by Scanning Transmission Electron Microscopy (STEM), in situ synchrotron X-ray Absorption Spectroscopy (XAS), and in situ synchrotron X-ray diffraction (XRD), which help elucidate the improved catalyst performance upon the introduction of Cu.

<table><tbody><tr><td>1&quot; quartz tube reactor&amp;nbsp;</td><td>Quartz Scientific</td><td>Processed by glass blower</td><td></td></tr><tr><td>drying oven&amp;nbsp;</td><td>Fisher Scientific</td><td></td><td></td></tr><tr><td>calcination Furnace</td><td>Thermo Sciencfic</td><td></td><td></td></tr><tr><td>clam-shell temperature programmed furnace&amp;nbsp;</td><td>Applied Test System</td><td>Custom made</td><td></td></tr><tr><td>propane dehydorgenation performance evaluation system</td><td></td><td>Homemade</td><td></td></tr><tr><td>gas chromatography</td><td>Hewlett-Packard</td><td>Model 7890</td><td></td></tr><tr><td>TEM grid</td><td>TedPella</td><td>01824G</td><td></td></tr><tr><td>pellet press</td><td>International Crystal Lab</td><td>0012-8211</td><td></td></tr><tr><td>die set</td><td>International Crystal Lab</td><td>0012-189</td><td></td></tr><tr><td>Linkam Sample Stage</td><td>Linkam Scientific</td><td>Model TS1500</td><td></td></tr><tr><td>copper nitrate trihydrgate</td><td>Sigma Aldrich</td><td>61197</td><td></td></tr><tr><td>tetraammineplatinum nitrate&amp;nbsp;</td><td>Sigma Aldrich</td><td>278726</td><td></td></tr><tr><td>ammonia&amp;nbsp;</td><td>Sigma Aldrich</td><td>294993</td><td></td></tr><tr><td>silica</td><td>Sigma Aldrich</td><td>236802</td><td></td></tr><tr><td>isopropyl alcohol</td><td>Sigma Aldrich</td><td></td><td></td></tr><tr><td>balance</td><td>Denver Instrument Company</td><td>A-160</td><td></td></tr><tr><td>spatulas</td><td>VWR</td><td></td><td></td></tr><tr><td>ceramic and glass evaporating dishes, beakers</td><td>VWR</td><td></td><td></td></tr><tr><td>heating plate</td><td></td><td></td><td></td></tr><tr><td>kimwipe papers</td><td></td><td></td><td></td></tr><tr><td>mortar and pestle</td><td></td><td></td><td></td></tr><tr><td>quartz wool&amp;nbsp;</td><td></td><td></td><td></td></tr><tr><td>Swagelok tube fittings&amp;nbsp;</td><td></td><td></td><td></td></tr></tbody></table>

synthesis and testing of supported pt-cu solid solution nanoparticle catalysts for propane dehydrogenation

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are demonstrated here. The catalyst forms a substitutional solid solution structure, with a small and uniform particle size around 2 nm. This is realized by careful control over the impregnation, calcination, and reduction steps during catalyst preparation and is identified by advanced in situ synchrotron techniques. The catalyst propane dehydrogenation performance continuously improves with increasing Cu:Pt atomic ratio.

The propylene selectivity versus time for Pt and Pt-Cu catalysts measured at an initial propane conversion of about 20% is presented in Figure 1A. Pt catalyst has an initial selectivity of 61%, which increases to about 82% with time on-stream as the catalyst deactivates for 1h. The Pt-0.7Cu catalyst shows a better initial propylene selectivity of 72%. For Pt-2.3Cu and Pt-7.3Cu catalysts, their initial selectivity reach 90% and 96%, respectively, and are maint...

Watch this Scientific Journal Video about Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation at JoVE.com

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

A convenient method for the synthesis of 2 nm supported bimetallic nanoparticle Pt-Cu catalysts for propane dehydrogenation is reported here. In situ synchrotron X-ray techniques allow for the determination of the catalyst structure, which is typically unobtainable using laboratory instruments.

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are ...

synthesis-testing-supported-pt-cu-solid-solution-nanoparticle

Universidad de Cartagena UDEC

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JoVE Journal

Chemistry

11.9K Views.  Purdue University. A convenient method for the synthesis of 2 nm supported bimetallic nanoparticle Pt-Cu catalysts for propane dehydrogenation is reported here. In situ synchrotron X-ray techniques allow for the determination of the catalyst structure, which is typically unobtainable using laboratory instruments.

Video: Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

On the Preparation and Testing of Fuel Cell Catalysts Using the Thin Film Rotating Disk Electrode Method

We present a step-by-step tutorial to prepare proton exchange membrane fuel cell (PEMFC) catalysts, consisting of Pt nanoparticles (NPs) supported on a high surface area carbon, and to test their performance in thin film rotating disk electrode (TF-RDE) measurements. The TF-RDE methodology is widely used for catalyst screening; nevertheless, the measured performance sometimes considerably differs among research groups. These uncertainties impede the advancement of new catalyst materials and, consequently, several authors discussed possible best practice methods and the importance of benchmarking.
The visual tutorial highlights possible pitfalls in the TF-RDE testing of Pt/C catalysts. A synthesis and testing protocol to assess standard Pt/C catalysts is introduced that can be used together with polycrystalline Pt disks as benchmark catalysts. In particular, this study highlights how the properties of the catalyst film on the glassy carbon (GC) electrode influence the measured performance in TF-RDE testing. To obtain thin, homogeneous catalyst films, not only the catalyst preparation, but also the ink deposition and drying procedures are essential. It is demonstrated that an adjustment of the ink&#39;s pH might be necessary, and how simple control measurements can be used to check film quality. Once reproducible TF-RDE measurements are obtained, determining the Pt loading on the catalyst support (expressed as Pt wt%) and the electrochemical surface area is necessary to normalize the determined reaction rates to either surface area or Pt mass. For the surface area determination, so-called CO stripping, or the determination of the hydrogen underpotential deposition (Hupd) charge, are standard. For the determination of the Pt loading, a straightforward and cheap procedure using digestion in aqua regia with subsequent conversion of Pt(IV) to Pt(II) and UV-vis measurements is introduced.

Preparing and testing Pt/C fuel cell catalysts is subject to continuous discussion in the scientific community with respect to reproducibility and best practice. With the presented work, we intend to present a step-by-step tutorial to make and test Pt/C catalysts, which can serve as benchmark for novel catalyst systems.

We present a step-by-step tutorial to prepare proton exchange membrane fuel cell (PEMFC) catalysts, consisting of Pt nanoparticles (NPs) supported on a ...

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Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of Chalcogenidoplumbates(II or IV)

The phases of &#34;PbCh2&#34; (Ch = Se, Te) are obtained from solid-state syntheses (i.e., by the fusion of the elements under inert conditions in silica glass ampules). Reduction of such phases by elemental alkaline metals in amines affords crystalline chalcogenidoplumbate(II) salts comprised of [PbTe3]2- or [Pb2Ch3]2- anions, depending upon which sequestering agent for the cations is present: crown ethers, like 18-crown-6, or cryptands, like [2.2.2]crypt. Reactions of solutions of such anions with transition-metal compounds yield (poly-)chalcogenide anions or transition-metal chalcogenide clusters, including one with a &#181;-PbSe ligand (i.e., the heaviest-known CO homolog).
In contrast, the solid-state synthesis of a phase of the nominal composition &#34;K2PbSe2&#34; by successive reactions of the elements and by the subsequent solvothermal treatment in amines yields the first non-oxide/halide inorganic lead(IV) compound: a salt of the ortho-selenidoplumbate(IV) anion [PbSe4]4-. This was unexpected due to the redox potentials of Pb(IV) and Se(-II). Such methods can further be applied to other elemental combinations, leading to the formation of solutions with binary [HgTe2]2- or [BiSe3]3- anions, or to large-scale syntheses of K2Hg2Se3 or K3BiSe3 via the solid-state route.
All compounds are characterized by single-crystal X-ray diffraction and elemental analysis; solutions of plumbate salts can be investigated by 205Pb and 77Se or 127Te NMR techniques. Quantum chemical calculations using density functional theory methods enable energy comparisons. They further allow for insights into the electronic configuration and thus, the bonding situation. Molecular Rh-containing Chevrel-type compounds were found to exhibit delocalized mixed valence, whereas similar telluridopalladate anions are electron-precise; the cluster with the &#181;-PbSe ligand is energetically favored over a hypothetical CO analog, in line with the unsuccessful attempt at its synthesis. The stability of formal Pb(IV) within the [PbSe4]4- anion is mainly due to a suitable stabilization within the crystal lattice.

Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of ChalcogenidoplumbatesII or IV

The synthesis of chalcogenidoplumbates(II,IV) via the in situ reduction of nominal "PbCh2" (Ch = Chalcogen) and via a solid-state reaction and subsequent solvothermal reactions is presented. Additionally, reactivities of plumbate(II) solutions are portrayed, which yield the heaviest-known CO homolog known to date: the &#181;-PbSe ligand.

The phases of &#34;PbCh2&#34; (Ch = Se, Te) are obtained from solid-state syntheses (i.e., by the fusion of the elements under inert conditions in silica ...

Measurement of Particle Size Distribution in Turbid Solutions by Dynamic Light Scattering Microscopy

A protocol for measuring polydispersity of concentrated polymer solutions using dynamic light scattering is described. Dynamic light scattering is a technique used to measure the size distribution of polymer solutions or colloidal particles. Although this technique is widely used for the assessment of polymer solutions, it is difficult to measure the particle size in concentrated solutions due to the multiple scattering effect or strong light absorption. Therefore, the concentrated solutions should be diluted before measurement. Implementation of the confocal optical component in a dynamic light scattering microscope1 helps to overcome this barrier. Using such a microscopic system, both transparent and turbid systems can be analyzed under the same experimental setup without a dilution. As a representative example, a size distribution measurement of a temperature-responsive polymer solution was performed. The sizes of the polymer chains in an aqueous solution were several tens of nanometers at a temperature below the lower critical solution temperature (LCST). In contrast, the sizes increased to more than 1.0 &#181;m when above the LCST. This result is consistent with the observation that the solution turned turbid above the LCST.

A protocol for the direct measurement of particle size distribution in concentrated solutions using dynamic light scattering microscopy is presented.

A protocol for measuring polydispersity of concentrated polymer solutions using dynamic light scattering is described. Dynamic light scattering is a ...

Protocol for the Solid-phase Synthesis of Oligomers of RNA Containing a 2'-O-thiophenylmethyl Modification and Characterization via Circular Dichroism

Solid-phase synthesis has been used to obtain canonical and modified polymers of nucleic acids, specifically of DNA or RNA, which has made it a popular methodology for applications in various fields and for different research purposes. The procedure described herein focuses on the synthesis, purification, and characterization of dodecamers of RNA 5&#39;-[CUA CGG AAU CAU]-3&#39; containing zero, one, or two modifications located at the C2&#39;-O-position. The probes are based on 2-thiophenylmethyl groups, incorporated into RNA nucleotides via standard organic synthesis and introduced into the corresponding oligonucleotides via their respective phosphoramidites. This report makes use of phosphoramidite chemistry via the four canonical nucleobases (Uridine (U), Cytosine (C), Guanosine (G), Adenosine (A)), as well as 2-thiophenylmethyl functionalized nucleotides modified at the 2&#39;-O-position; however, the methodology is amenable for a large variety of modifications that have been developed over the years. The oligonucleotides were synthesized on a controlled-pore glass (CPG) support followed by cleavage from the resin and deprotection under standard conditions, i.e., a mixture of ammonia and methylamine (AMA) followed by hydrogen fluoride/triethylamine/N-methylpyrrolidinone. The corresponding oligonucleotides were purified via polyacrylamide electrophoresis (20% denaturing) followed by elution, desalting, and isolation via reversed-phase chromatography (Sep-pak, C18-column). Quantification and structural parameters were assessed via ultraviolet-visible (UV-vis) and circular dichroism (CD) photometric analysis, respectively. This report aims to serve as a resource and guide for beginner and expert researchers interested in embarking in this field. It is expected to serve as a work-in-progress as new technologies and methodologies are developed. The description of the methodologies and techniques within this document correspond to a DNA/RNA synthesizer (refurbished and purchased in 2013) that uses phosphoramidite chemistry.

Protocol for the Solid-phase Synthesis of Oligomers of RNA Containing a 2'-O-thiophenylmethyl Modification and Characterization via Circular Dichroism

This article provides a detailed procedure on the solid-phase synthesis, purification, and characterization of dodecamers of RNA modified at the C2&#39;-O-position. UV-vis and circular dichroism photometric analyses are used to quantify and characterize structural aspects, i.e., single-strands or double-strands.

Solid-phase synthesis has been used to obtain canonical and modified polymers of nucleic acids, specifically of DNA or RNA, which has made it a popular ...

Liquid-cell Transmission Electron Microscopy for Tracking Self-assembly of Nanoparticles

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully understood. We have traced the trajectories of individual nanoparticles using liquid-cell transmission electron microscopy (TEM) to investigate the mechanism of the assembly process. Herein, we present the protocols used for liquid-cell TEM studies of the self-assembly mechanism. First, we introduce the detailed synthetic protocols used to produce uniformly sized platinum and lead selenide nanoparticles. Next, we present the microfabrication processes used to produce liquid cells with silicon nitride or silicon windows and then describe the loading and imaging procedures of the liquid-cell TEM technique. Several notes are included to provide helpful tips for the entire process, including how to manage the fragile cell windows. The individual motions of nanoparticles tracked by liquid-cell TEM revealed that changes in the solvent boundaries caused by evaporation affected the self-assembly process of nanoparticles. The solvent boundaries drove nanoparticles to primarily form amorphous aggregates, followed by flattening of the aggregates to produce a 2-dimensional (2D) self-assembled structure. These behaviors are also observed for different nanoparticle types and different liquid-cell compositions.

Here we introduce experimental protocols for the real-time observation of a self-assembly process using liquid-cell transmission electron microscopy.

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully ...

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of NixNb1-xO nanoparticles with different atomic compositions (x = 0.03, 0.08, 0.15, and 0.20) have been prepared by chemical precipitation. These NixNb1-xO catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The study revealed the sponge-like and fold-like appearance of Ni0.97Nb0.03O and Ni0.92Nb0.08O on the NiO surface, and the larger surface area of these NixNb1-xO catalysts, compared with the bulk NiO. Maximum surface area of 173 m2/g can be obtained for Ni0.92Nb0.08O catalysts. In addition, the catalytic hydroconversion of lignin-derived compounds using the synthesized Ni0.92Nb0.08O catalysts have been investigated.

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

A protocol for the synthesis of sponge-like and fold-like Ni1-xNbxO nanoparticles by chemical precipitation is presented.

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of ...

Synthesis of Bimetallic Pt/Sn-based Nanoparticles in Ionic Liquids

We demonstrate a method for the synthesis of bimetallic nanoparticles consisting of Pt and Sn. A synthesis strategy is used in which the particular physico-chemical properties of ionic liquids (ILs) are exploited to control both nucleation and growth processes. The nanoparticles form colloidal sols of very high colloidal stability in the IL, which is particularly interesting in view of their use as quasi-homogeneous catalysts. Procedures for both nanoparticle extraction in conventional solvents and for nanoparticle precipitation are presented. The size, structure and composition of the synthesized nanocrystals are confirmed using inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDX). By this, we show that the nanocrystals are random-type alloy and of small (2-3 nm) size. The catalytic activity and selectivity in the hydrogenation of &#945;,&#946;-unsaturated aldehydes is tested in a semi-continuous batch-type reactor. In this context, the bimetallic Pt/Sn-based nanoparticles reveal a high selectivity towards the unsaturated alcohol.

A protocol for the synthesis of bimetallic nanoparticles in ionic liquids and the procedure of their catalytic testing in the selective hydrogenation of unsaturated aldehydes are described.

We demonstrate a method for the synthesis of bimetallic nanoparticles consisting of Pt and Sn. A synthesis strategy is used in which the particular ...

Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid nanosheets, a series of Pt/xHMNO6/CNTs with different solid acid compositions (x = 5, 20 wt%; M = Nb, Ta; N = Mo, W) have been prepared by carbon nanotube pretreatment, protonic exchange, solid acid exfoliation, aggregation and finally Pt particles impregnation. The Pt/xHMNO6/CNTs are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and NH3-temperature programmed desorption. The study revealed that HNbWO6 nanosheets were attached on CNTs, with some edges of the nanosheets being bent in shape. The acid strength of the supported Pt catalysts increases in the following order: Pt/CNTs &#60; Pt/5HNbWO6/CNTs &#60; Pt/20HNbMoO6/CNTs &#60; Pt/20HNbWO6/CNTs &#60; Pt/20HTaWO6/CNTs. In addition, the catalytic hydroconversion of lignin-derived model compound: diphenyl ether using the synthesized Pt/20HNbWO6 catalyst has been investigated.

A protocol for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs is presented.

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid ...

Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

A method for facile synthesis of nanostructured catalysts supported on carbon nanotubes with atomically dispersed cobalt and nitrogen dopant is presented herein. The novel strategy is based on a facile one-pot pyrolysis treatment of cobalt (II) acetylacetonate and nitrogen-rich organic precursors under Ar atmosphere at 800 &#176;C, resulting in the formation of Co- and N- co-doped carbon nanotube with earthworm-like morphology. The obtained catalyst was found to have a high density of defect sites, as confirmed by Raman spectroscopy. Here, cobalt (II) nanoparticles were stabilized on the atomically dispersed cobalt- and nitrogen-doped carbon nanotubes. The catalyst was confirmed to be effective in the catalytic hydrolysis of ammonia borane, in which the turnover frequency was 5.87 mol H2&#183;molCo-1&#183;min-1, and the specific hydrogen generation rate was determined to be 2447 mL H2&#183;gCo-1&#183;min-1. A synergistic function between the Co nanoparticle and the doped carbon nanotubes was proposed for the first time in the catalytic hydrolysis of ammonia borane reaction under a mild condition. The resulting hydrogen production with its high energy density and minimal refueling time could be suitable for future development as energy sources for mobile and stationary applications such as road trucks and forklifts in transport and logistics.

Here, we present a protocol to synthesize Co nanoparticles supported on carbon nanotubes with Co- and N- dopants for hydrogen productions.

A method for facile synthesis of nanostructured catalysts supported on carbon nanotubes with atomically dispersed cobalt and nitrogen dopant is presented ...

Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania During Hydrogenation of Alkenes and Aldehydes

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands like amines are removed by diverse pre-treatment procedures before use in heterogeneous catalysis as amines are considered as a catalyst poison. However, a possible beneficial influence of these surface modifiers on hydrogenation reactions, which is known from spectator species on metal surfaces, is often neglected.
Therefore, amine-stabilized Pt nanoparticles supported by titania (P25) were used without any pre-treatment in order to elucidate a possible influence of the ligand in liquid phase hydrogenation reactions. The catalytic activity of amine-stabilized Pt nanoparticles of two different sizes was investigated in a double-walled stirring tank reactor at 69 &#176;C to 130 &#176;C and 1 atm hydrogen pressure. The conversion of cyclohexene to cyclohexane was determined by gas chromatography (GC) and was compared to ligand-free Pt particles. All catalysts were checked before and after reaction by transmission electron spectroscopy (TEM) and X-ray photoelectron spectroscopy (XPS) for possible changes in size, shape, and ligand shell. The hydrogenation of cyclohexene in liquid phase revealed a higher conversion for amine-stabilized Pt nanoparticles on titania than the ligand-free particles. The hydrogenation of 5-methylfurfural (5-MF) was chosen for a further test reaction, since the hydrogenation of &#945;, &#946;-unsaturated aldehydes is more complex and exhibits various reaction paths. However, XPS and infrared spectroscopy (IR) proved that 5-MF acts as catalyst poison at the given reaction conditions.

This protocol shows a convenient method for comparing the catalytic properties of supported platinum catalysts, synthesized by deposition of nanosized colloids or by impregnation. The hydrogenation of cyclohexene serves as a model reaction to determine the catalytic activity of the catalysts.

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands ...

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

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On the Preparation and Testing of Fuel Cell Catalysts Using the Thin Film Rotating Disk Electrode Method

Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of Chalcogenidoplumbates(II or IV)

Measurement of Particle Size Distribution in Turbid Solutions by Dynamic Light Scattering Microscopy

Protocol for the Solid-phase Synthesis of Oligomers of RNA Containing a 2'-O-thiophenylmethyl Modification and Characterization via Circular Dichroism

Liquid-cell Transmission Electron Microscopy for Tracking Self-assembly of Nanoparticles

Chemical Precipitation Method for the Synthesis of Nb₂O₅ Modified Bulk Nickel Catalysts with High Specific Surface Area

Synthesis of Bimetallic Pt/Sn-based Nanoparticles in Ionic Liquids

Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania During Hydrogenation of Alkenes and Aldehydes