The Effect of Surface Functional Groups on the Dispersion, Chemical Properties, and Catalytic Behavior of Carbon- Supported Pd and Pt-Sn Catalysts Prepared from Metal Cluster

研究了不同含氧官能团对钯在碳上的分散性、耐烧结性和催化性能的影响，以及铂锡在碳上的催化行为。其策略是以受控的方式改变高纯度碳上的羧基、内酯、羰基、羟基和酚基的浓度。从历史上看，对碳表面进行表征的难度一直令这方面的尝试受挫。本研究采用反射红外光谱、热重分析/质谱仪和差示微量热法对碳表面进行了表征，分别用1000℃去除所有表面基团和空气、硝酸和过氧化氢处理后选择性地恢复某些基团。制备金属/碳催化剂的新方法包括合成和浸渍在低温下容易还原的钯和铂-锡有机金属络合物。通过磁化率测量、氧、一氧化碳和氢在金属表面的吸附热、化学吸附一氧化碳的红外光谱以及化学吸附的氢和钯-105的固态魔角旋转核磁共振，确定了钯微晶尺寸对磁性和化学性质的影响。这项工作直接涉及到碳负载贵金属催化剂的性能，但结果也与碳电极的生产和使用、煤炭气化和石油重整有关。碳载贵金属催化剂广泛应用于特种化学品和石油化工等行业。

This is a study of the effects of different oxygen-containing functional groups on the dispersion, sinter resistance, and catalytic behavior of palladium on carbon and of platinum-tin on carbon. The strategy is to alter, in a controlled way, the concentrations of carboxyl, lactone, carbonyl, hydroxyl, and phenolic groups on a high-purity carbon. Historically, attempts to do this have been frustrated by the difficulty of characterizing carbon surfaces. In this study, carbon surfaces are characterized by reflection infrared spectroscopy, thermal gravimetric analysis /mass spectrometry, and differential microcalorimetry after treatment at 1000> to remove all surface groups and after treatments in air, nitric acid, and hydrogen peroxide to selectively restore certain groups. Novel approaches to the preparation of metal/carbon catalysts involve the synthesis and impregnation of palladium and platinum-tin organometallic complexes that can be easily reduced at low temperatures. The influence of palladium crystallite size on magnetic and chemical properties is determined by magnetic susceptibility measurements, heats of adsorption for oxygen, carbon monoxide, and hydrogen on the metal, infrared spectra of chemisorbed carbon monoxide, and solid-state magic-angle-spinning nuclear magnetic resonance of chemisorbed hydrogen as well as palladium-105. The work addresses directly the performance of carbon- supported noble-metal catalysts, but the results are also relevant to production and use of carbon electrodes, coal gasification, and petroleum reforming. Carbon-supported noble-metal catalysts are widely used in the specialty chemicals and petrochemicals industries.