期刊
Catalysis Science & Technology
卷 6, 期 18, 页码 6965-6976出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c6cy00491a
关键词
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资金
- School of Chemical Engineering, Purdue University
- Kirk Endowment Exploratory Research Recharge Grant
- U.S. Department of Energy, Office of Basic Energy Sciences [DE-AC02-06CH11357]
- Department of Energy
- MRCAT
Silica supported Pd and Pd-In catalysts with different In : Pd atomic ratios and similar particle size (similar to 2 nm) were tested for ethane dehydrogenation at 600 degrees C. For a monometallic Pd catalyst, at 15% conversion, the dehydrogenation selectivity and initial turnover rate (TOR, per surface Pd site) were 53% and 0.03 s(-1), respectively. Addition of In to Pd increased the dehydrogenation selectivity to near 100% and the initial TOR to 0.26 s(-1). Carbon monoxide IR, in situ synchrotron XAS and XRD analysis showed that for Pd-In catalysts with increasing In loading, different bimetallic structures were formed: at low In loading a fraction of the nanoparticle surface was transformed into PdIn intermetallic compound (IMC, also known as intermetallic alloy) with a cubic CsCl structure; at higher In loading, a Pd-core/PdIn-shell structure was formed and at high In loading the nanoparticles were pure PdIn IMC. While a Pd metal surface binds CO predominantly in a bridge fashion, the PdIn IMC predominantly binds CO linearly. Formation of the PdIn IMC structure on the catalyst surface geometrically isolates the Pd catalytic sites by non-catalytic, metallic In neigh-bors, which is suggested to be responsible for the high olefin selectivity. Concomitant electronic effect due to Pd-In bond formation likely leads to the increase in TOR. Though multiple IMC structures with different atomic ratios are possible for the Pd-In binary system, only a cubic PdIn IMC with CsCl structure was observed, implying a kinetically controlled solid state IMC formation mechanism.
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