The Reactivity of Multifunctional Alcohols on Palladium Surfaces and Supported Catalysts.

摘要

In recent years there has been an increased interest in the development of sustainable processes for the conversion of renewable resources into useful products. Among the most promising of these is the upgrading of multifunctional alcohols with palladium catalysts. We present here an investigation into the fundamental mechanistic details associated with the conversion of these molecules as well as routes towards the development of improved industrial catalysts.;Ethylene glycol and 1,2-propanediol are important biorefining intermediates and serve as probe molecules for more complex polyols. By utilizing surface science techniques we have gained molecular level insight into the interactions of these molecules with a Pd(111) single crystal surface. The results show evidence that adjacent functional groups on multifunctional alcohols can influence each other, leading to reactions that are not observed from their simple alcohol analogues.;Studying 2-iodoethanol provides insight into how the presence of halogen catalyst modifiers affects the reactivity of multifunctional alcohols. In this investigation, iodine was observed to influence the adsorption geometry and reaction selectivity of the hydroxyethyl intermediate. In order to better understand this effect, 1-propanol and 2-propanol were studied on Pd(111) pre-covered with varying amounts of iodine. The results suggest that blocking active sites with strongly adsorbed catalyst modifiers can have large effects on the reactivity of multifunctional alcohols.;The utilization of bimetallic catalysts is another way to influence reactivity. By studying the oxidation of ethylene glycol and 1,2-propanediol on Pd/C, Au/C and Au-Pd/C we have gained insight into bimetallic effects, which are associated with a significant increase in catalytic activity. Experiments with isotopically labeled reagents show that C-H bond scission is the rate-limiting step, and computational modeling suggested that an altered electronic structure may be responsible for the increased catalytic performance.