Thermal Hysteresis of Palladium encaged inside Mesoporous Silica catalyst for Low Temperature CO oxidation

Abstract

Thermal Hysteresis of Palladium encaged inside Mesoporous Silica catalyst for Low Temperature CO oxidation Rola Al Soubaihi 1,2, Joydeep Dutta2 Liberal Arts and Science Program, Virginia Commonwealth University-Qatar, Doha, Qatar Department of Applied Physics, KTH Royal Institute of Technology, Stockholm, Sweden Carbon Monoxide (CO) is colorless, odorless gas produced from incomplete combustion of carbon fuel under conditions with a limited supply of oxygen. Catalytic oxidation is one of the effective methods of removing CO and convert it to CO2. [1] Catalyzed CO oxidation reaction finds applications in many fields such as environmental protection, air purification for buildings or cars, orbiting, closed-cycle CO2 lasers, gas masks for mining applications, CO detectors[2-3]. Depending on their size, shape, and preparation conditions, Nanocatalysts can exhibit unique properties (electrical, optical, magnetic, and catalytic) which are different from their bulk material properties [4-6]. The surface of nanomaterials contains large number of high energy defects such as surface and edge atoms that can provide active sites for catalyzing surface reactions by lowering the activation energy [7-8]. Supported Palladium catalysts are known for their high activity, recyclability, and their cheap cost when compared to platinum catalysts. Support plays a crucial role in the synthesis of such catalysts. In this regard support can reduce the amounts of the metal and ensure a good dispersion, and increase their thermal stability. Mesoporous materials with large internal surface areas (>1000 m2/g) and narrow pore size distributions can be an ideal support for Palladium based catalysts [9-10]. Silica are well known for structural and thermal properties and allow anchoring of catalytically palladium active species onto their surfaces. Silica can provide enormous beneficial features to enhance the catalytic activity such as high surface area, high porous, high thermal insulation, and local heating and heat retention [11-13]. Here, we report for the first time exceptional catalytic CO oxidation on Pd supported on mesoporous SiO2 with good stability and recycling behavior under heating and cooling conditions with wide CO Thermal hysteresis (close to 200 °C). We attribute our results to the phase transformation of Palladium to palladium oxide intermediate at different temperatures during the heating and cooling cycles and the structure and the local environment of the palladium since Pd clusters are small and highly dispersed on the silica surfaces and encaged inside the pores.