Water-Resistant Pt Sites in Hydrophobic Mesopores Effective for Low-Temperature Ethylene Oxidation
Water-Resistant Pt Sites in Hydrophobic Mesopores Effective for Low-Temperature Ethylene Oxidation
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DOI：
10.1021/acscatal.0c02816
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发表时间：
2020-11-20
期刊：
影响因子：
12.9
通讯作者：
Fukuoka, Atsushi
中科院分区：
文献类型：
--
作者：
Satter, Shazia S.;Hirayama, Jun;Fukuoka, Atsushi
采用固定床流动反应器和傅里叶变换红外（FTIR）原位表征技术，在0℃条件下研究了二氧化硅负载Pt催化剂在50 ppm乙烯有氧氧化中的构效关系。所有Pt催化剂的活性都被乙烯在化学计量氧化过程中形成的水分子所降低，并逐渐稳定下来。介孔二氧化硅负载的Pt催化剂在800℃的空气中煅烧后，其稳态活性得到改善，而非多孔二氧化硅负载的Pt催化剂则没有这种效果。co脉冲滴定、水吸附测量、Si-29 MAS NMR和原位红外光谱以及催化活性研究表明，介孔硅负载Pt催化剂的活性高于无孔硅负载Pt催化剂，尽管具有相似的疏水性和较低的Pt分散。使用CO作为分子探针的原位表征表明，即使在催化剂表面完全水化后，疏水介孔内的Pt表面的一部分也不参与物理吸附水分子和表面SiOH基团之间的氢键网络，并且裸露的Pt位点有望更有效地用于乙烯氧化。这种“疏水Pt表面”只能在疏水介孔二氧化硅载体上形成，这可能是因为Pt纳米颗粒完全被疏水硅氧烷网络包围。由缩合硅氧烷网络和有限的介孔形成的独特环境是Pt纳米颗粒低温氧化痕量乙烯的高活性的主要原因。
The structure-activity relationship of silica-supported Pt catalysts in aerobic oxidation of 50 ppm ethylene was studied at 0 degrees C with a fixed-bed flow reactor and in situ characterization techniques using Fourier-transform infrared (FTIR) spectroscopy. The activity of all Pt catalysts examined here decreased by water molecules formed during stoichiometric oxidation of ethylene and became stable steadily. A mesoporous silica-supported Pt catalyst improved its steady-state activity after calcination of the support in air at 800 degrees C, whereas no such effect was observed for a nonporous silica support. CO-pulse titration, H2O adsorption measurements, Si-29 MAS NMR, and in situ FTIR along with catalytic activity studies revealed that the activity of the mesoporous silica-supported Pt catalyst is higher than that of nonporous silica-supported ones, despite showing similar hydrophobicity and low Pt dispersion. In situ characterization using CO as a molecular probe indicates that a part of the Pt surface inside hydrophobic mesopores is not involved in the hydrogenbonding network among physisorbed water molecules and surface SiOH groups even after full hydration of the catalyst surface, and bare Pt sites are expected to work more effectively for ethylene oxidation. Such a "hydrophobic Pt surface" can only be formed on a hydrophobic mesoporous silica support, which is probably because of Pt nanoparticles surrounded by a hydrophobic siloxane network entirely. A unique environment derived from the condensed siloxane network and restricted mesopores contributes largely to the high activity of Pt nanoparticles for low-temperature oxidation of trace ethylene.