Galvanic Synthesis and In Situ Speciation of Methane Oxidation Catalysts

Abstract

The focus of this thesis is the methane oxidation reaction, catalyzed by Pd nanoparticles on a metal oxide support. This thesis presents a synthesis strategy for dispersing Pd catalysts on metal oxide supports and in situ speciation of these catalysts, therefore, will be presented in two parts. Firstly, a unique synthetic process will be presented for the synthesis of metal nanoparticles on metal oxide supports: galvanic deposition. Following this, in situ X-ray Absorption Spectroscopy (XAS) analysis of supported Pd nanoparticles is performed in order to determine speciation of both the metal and support during methane oxidation reactions. In Chapter 2 a synthetic procedure for the synthesis of Pd on SnO is presented and the resulting materials are thoroughly characterized. The synthetic procedure is termed galvanic deposition and involves a spontaneous galvanic reaction between the Pd salt and metal oxide. A case study will be presented targeting a Pd on SnO2 catalyst, synthesized via Pd(II) salts and SnO. The case study is finalized with the characterization of galvanically synthesized Pd/SnO2 catalysts at competitive dispersions with modern literature. The chapter will include an argument for the use of the technique, a discussion of the specific problems for the technique and will finish with an exploration of the generality of the technique. Chapter 3 discusses in situ XAS work performed at the Canadian Light Source on Pd-based catalysts for methane oxidation reactions. In situ Pd speciation on a variety of metal oxide supports is followed at temperatures up to 450 oC. The Pd, PdO, and Pd(OH)2 equilibrium is of interest as the presence of PdO is required for methane oxidation, the presence of Pd is beneficial for methane oxidation and the presence of Pd(OH)2 has been shown to passivate methane oxidation catalysts. Direct measurements of Pd(OH)2 in situ have remained elusive in literature. This work presents speciation and quantification of Pd, PdO, and Pd(OH)2 on three diverse Pd on metal oxide systems at both the Pd K and L3 edges. Quantification allows comparison and analysis of Pd speciation in situ and thereby provides a tool necessary to further understand metal-metal oxide structure-property relationships.