Low-Temperature CO Oxidation: Effect of the Second Metal on Activated Carbon Supported Pd Catalysts

Abstract: Activated carbon (AC) supported monometallic Pd and bimetallic Pd-M (M = Co, Ni, and Cu) catalysts were prepared by impregnation-reduction method and investigated for carbon monoxide (CO) oxidation. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed highly disperse Pd-M nanoparticles (~ 3–5 nm) on the AC support. The addition of the second transition metal in Pd/AC resulted in an increase in the specific surface area and smaller average particle size. CO oxidation experiments were carried out in a vertical fixed-bed quartz reactor at gas hourly space velocity (GHSV) of 30,000 h^{− 1} under atmospheric pressure. The catalytic order is as follows: Pd–Cu/AC > Pd–Ni/AC > Pd–Co/AC > Pd/AC. The T₅₀ (50% CO conversion) value of Pd–Cu/AC and Pd/AC catalysts are 30 and 70 °C. BET, XRD and TEM analysis of the used Pd-M/AC and Pd/AC catalysts were performed in order to find any change in the specific surface area, structure, morphology, and average particle size of the catalysts after CO oxidation. The results showed that the bimetallic Pd-M/AC catalysts had better catalytic activity and stability than the monometallic Pd/AC catalyst. Pd–Cu/AC showed excellent time-on-stream stability of 50 h. The apparent activation energy of the Pd–Cu/AC is found to be 69.32 kJ mol^{− 1}. Thus, bimetallic Pd-M/AC catalysts have a potential for practical CO oxidation reaction. Graphical Abstract: [Figure not available: see fulltext.].