Design of Sulfur Tolerant Transition Metal Catalysts and Oxide Based Oxygen Evolution Electrocatalysts.

摘要

In chemical industry, one of the main challenges is to improve the activity and selectivity of heterogeneous catalysts by designing new materials. The catalytic properties of a transition metal can be altered by alloying the metal catalyst with another metal; or by utilizing it in its transition metal oxide form where the idea of mixed metals can be utilized as well. The mentioned catalytic changes are in many cases, due to the modifications in the electronic structure of the transition metal system since the electronic characteristics are the key factors determining the activity and selectivity of many of the late transition metal based heterogeneous catalysts. Therefore, establishing a basic understanding of the electronic structures of the catalysts, understanding how the surface electronic structure varies due to alloying, effects of adsorbate coverage, and the mixed metals in metal oxides is essential to understand the variations in the catalytic properties of the systems. The main objective of this dissertation is to utilize an atomistic level approach to develop an understanding of the modifications in the electronic characteristics of the transition metal based catalysts. The presented approach provides a critical development towards the rational design of new bimetallic systems with desirable electronic and thus, chemical properties. This is illustrated, for determining sulfur tolerant metallic systems and designing transition metal based oxides for oxygen evolution reaction.;As being one of most challenging processes in the chemical industry, sulfur poisoning of a transition metal based catalyst has been studied and changes in the reactivity of the catalyst have been explained through the adsorbate-induced modifications in the electronic structures of the metal system. We present a tight-bonding approach, parameterized by a database of density functional theory calculations to model the effect of simple adsorbates and alloying on the surface electronic characteristics. The proposed model could be used as a first step towards predicting the properties of transition metal based systems and designing surface structures with desirable electronic and thus chemical properties. We demonstrate the feasibility of the proposed model by identifying sulfur tolerant bimetallic surfaces using a screening approach.;Similar to the understanding in the reactivities of metallic systems, it is desirable to establish activity-structure relation for transition metal oxide based systems. To tackle the problem, computational experiments have been performed to study the oxygen evolution reaction (OER) in detail over oxide surfaces. The findings of the computational approach have guided the experimental studies where high surface area mixed-metal oxide catalysts with enhanced reactivity were synthesized for the OER.