Heterogeneous catalysis including solid-gas/solid-liquid/liquid-gas reactions contributes largely to the production of chemical feedstocks and energy sources. For example, the total/partial oxidation of alcohols is very important for fuel cells and fine chemical synthesis.1,2) Actually, many catalytic alcohol oxidation reactions in industry are performed in liquid phase, but their reaction kinetics and mechanisms are not as well understood as those in gas phase. Previously, we found that Pt nanoparticles (NPs) could catalyze the oxidation of methanol, ethanol, and iso-propanol in both gas and liquid phases3-5). We observed several discrepancies between the two phases such as the reaction rates, apparent activation energies (Ea) and H2O effects, which were attributed to the molecular orientation at catalyst surface in each phase.4,5) Herein, the catalytic 1-propanol oxidation by O2 on size-controlled Pt NPs has been studied in detail, which will broaden our knowledge in the differences of alcohol oxidation at solid-gas/solid-liquid interfaces. The Pt NPs (2-7 nm) were prepared by colloidal method and loaded into mesoporous silica (MCF-17). For gas phase 1-propanol oxidation, the products were propanal (75-85%) and CO2 (15-25%) at 60-80 oC, while in the liquid phase the propanal selectivity was always above 99%. Both the gas and liquid phase reactions showed obvious size-dependence, with higher reaction rate obtained on larger Pt NPs. With similar reactant concentrations, the gas phase reaction rate was much higher than that in the liquid phase. Yet, the Ea for the gas phase reaction (123 KJ/mol) was much higher than that in the liquid phase (29 KJ/mol). More interestingly, H2O greatly inhibited the gas phase reaction with increased Ea (154 KJ/mol), while H2O significantly promoted the liquid phase reaction with decreased Ea (8 KJ/mol). These results indicate that totally different reaction mechanisms are present for the catalytic 1-propanol oxidation on Pt/MCF-17 at solid-gas/solid-liquid interfaces, and the sum frequency generation spectroscopy study and theoretical calculations are under way to obtain a full understanding of the key factors influencing this reaction at molecular level. Reference 1) X. Zhao, et al., Energy Environ. Sci., 2011, 4, 2736. 2) T. Mallat, et al., Chem. Rev., 2004, 104, 3037. 3) H. Wang, et al., Catal. Lett., 2014, 144, 1930. 4) A. Sapi, et al., Nano Lett., 2014, submitted. 5) H. Wang, et al., J. Am. Chem. Soc., 2014, 136, 10515.

Different catalytic oxidation behaviors of 1-propanol on size-controlled platinum nanoparticles at solid-gas and solid-liquid interfaces

249th National Meeting (2015)

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