Reaction mechanism for selective synthesis of gasoline-range isoalkanes from syngas over RuPtHY zeolites. II. Role of metals and acid sites.
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Role of metals and acid site in selective synthesis of gasoline-range isoalkanes from syngas catalyzed by zeolite Y supported Ru–Pt alloy has been studied. As a probe molecule 1-alkene was added into syngas over the various combination of catalysts. Alloying Ru with Pt enhanced 1-octene conversion as well as CO conversion. Reaction of 1-octene over metal-free DAHY (dealuminated HY) zeolite produced cracking products with high selectivity for isobutanes; C<SUB>3</SUB><SUP>+</SUP> carbon number distribution was similar to that from CO hydrogenation over DAHY2R2P (Ru and Pt 2 wt%, respectively), suggesting that the selective formation of isoalkanes in gasoline-range from CO–H<SUB>2</SUB> over DAHY2R2P could be essentially due to acid-catalyzed reactions on zeolites. Cracking of 1-octene was affected by the support and increased in the order: NaY2R2P<HY2R2P<DAHY2R2P. Products via disproportionation were predominant for NaY2R2P and HY2R2P and those via simple cracking prevailed in DAHY2R2P. This could account for shift to light side in carbon number distribution from simple CO hydrogenation over DAHY2R2P. From syngas H<SUB>2</SUB>/CO ratio=13/2, methane was the main product. However, methane production was virtually unchanged on addition of 1-octene, implying that the presence of CO suppressed the hydrogenolysis of 1-octene on RuPt bimetallic site. Effects of contact time and temperature on selectivity for products were also discussed.