Name: synthesis and testing of supported pt-cu solid solution nanoparticle catalysts for propane dehydrogenation
Uploaded: 2017-07-18T15:00:00
Description: Watch this Scientific Journal Video about Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation at JoVE.com

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...

<ol>
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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.

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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 ...

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Solid-phase Synthesis of [4.4] Spirocyclic Oximes

A convenient synthetic route for spirocyclic heterocycles is well sought after due to the molecule&#39;s potential use in biological systems. By means of ...

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is designed and prepared ...

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 ...