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论文类型：期刊论文

发表时间：2018-09-01

发表刊物：ACS CATALYSIS

收录刊物：SCIE

卷号：8

期号：9

页面范围：8513-8524

ISSN号：2155-5435

关键字：atomic layer deposition; selective hydrogenation; platinum catalyst; unsaturated aldehydes; silica-alumina; infrared absorption spectroscopy; pyridine adsorption

摘要：Alumina-supported platinum catalysts have been modified with silicon oxide thin films grown using atomic layer deposition (ALD) in order to tune the acid-base and electronic properties of the oxide, and their performance has been tested for the hydrogenation of cinnamaldehyde. It was found that the silica layers greatly increase the stability of the platinum nanoparticles, preventing their sintering during high-temperature calcinations without affecting access to the metal surface in any significant way; the extent of CO adsorption, measured by infrared absorption spectroscopy was found to decrease by only one-third after 6 SiO2 ALD cycles. Additional Bronsted and Lewis acid sites were created upon the deposition of submonolayer coverages of silicon oxide, as probed via pyridine adsorption. The addition of the silicon oxide thin films reduced the overall activity of these catalysts but also increased their selectivity toward the production of the unsaturated alcohol. In addition, both turnover frequencies (TOFs) and selectivities were found to increase initially with reaction time in most cases, presumably the result of catalyst conditioning by the reaction mixture. Those improvements were seen to be retained upon recycling of the catalysts. The best catalysts in term of selectivity (>= 85% of cinnamyl alcohol production, in terms of TOFs) were obtained after 3 or 4 ALD cycles, which were estimated to deposit approximately half of a monolayer of SiO2. Based on these results, it is proposed that the added strong Bronsted acid sites at mixed Si-O-Al positions, possibly in synergy with the metal surface, may be responsible for the relative enhancement in the hydrogenation of C = O bonds detected.