Abstract
Catalytic oxidation of alcohols is an essential process for energy conversion, production of fine chemicals and pharmaceutical intermediates. Although it has been broadly utilized in industry, the basic understanding for catalytic alcohol oxidations at a molecular level, especially under both gas and liquid phases, is still lacking. In this paper, we systematically summarized our work on catalytic alcohol oxidation over size-controlled Pt nanoparticles. The studied alcohols included methanol, ethanol, 1-propanol, 2-propanol, and 2-butanol. The turnover rates of different alcohols on Pt nanoparticles and also the apparent activation energy in gas and liquid phase reactions were compared. The Pt nanoparticle size dependence of reaction rates and product selectivity was also carefully examined. Water showed very distinct effects for gas and liquid phase alcohol oxidations, either as an inhibitor or as a promoter depending on alcohol type and reaction phase. A deep understanding of different alcohol molecular orientations on Pt surface in gas and liquid phase reactions was established using sum-frequency generation spectroscopy analysis for in situ alcohol oxidations, as well as density functional theory calculation. This approach can not only explain the entirely different behaviors of alcohol oxidations in gas and liquid phases, but can also provide guidance for future catalyst/process design.
Highlights
Catalytic partial oxidation and complete oxidation of alcohols over platinum group metals (PGM) or metal oxide catalysts are fundamental processes in energy conversion, such as in fuel cells [1,2], and in fine chemical synthesis and the pharmaceutical industry [3,4,5,6,7]
Very few studies have focused on the systematic comparison on gas phase and liquid phase alcohol oxidations over the same PGM or metal oxide catalysts at the molecular level, which is very important for the basic understanding of the reaction kinetics and mechanisms to advance and improve the catalyst and process designs for practical application
Resultswould suggest that the reactionupon ratesdilution of catalytic resulting in much lower activity. These results suggest that the reaction rates of catalytic alcohol alcohol oxidation heavily depended on the reaction phase, and the oxidation heavily depended on the reaction phase, and the intrinsic intrinsic root cause for such discrepancy should be understood at the molecular level
Summary
Catalytic partial oxidation and complete oxidation of alcohols over platinum group metals (PGM) or metal oxide catalysts are fundamental processes in energy conversion, such as in fuel cells [1,2], and in fine chemical synthesis and the pharmaceutical industry [3,4,5,6,7]. Very few studies have focused on the systematic comparison on gas phase and liquid phase alcohol oxidations over the same PGM or metal oxide catalysts at the molecular level, which is very important for the basic understanding of the reaction kinetics and mechanisms to advance and improve the catalyst and process designs for practical application. Detailed comparisons of the reaction rates in both phases and the Pt nanoparticle size dependence of reaction rates, as well as product selectivity, the apparent activation energy of alcohol oxidations in both phases, and the response to co-existing water under different reaction conditions, are all included . To understand the intrinsic reasons at the molecular level for differences in reaction kinetics and mechanisms in alcohol oxidation under gas and liquid phases, the sum-frequency generation (SFG) vibrational spectroscopy measurements on Pt surface under reaction conditions were conducted and discussed in detail. In aid of density functional theory (DFT) computational modeling, different alcohol molecular orientations/configurations on
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