Influence of Ce/Zr Ratio on the Synergistic Effect over CuCe_1–xZr_xO_y/ZSM-5 Catalysts for the Self-Sustained Combustion of Carbon Monoxide

Abstract

The self-sustained combustion of CO was studied over a series of CuCe 1-x Zr x O y /ZSM-5 catalysts with different Ce/Zr molar ratios to evaluate the correlation of their structural characteristics with catalytic performance. The obtained results demonstrated that the activity of the cerium-containing catalysts was much higher than that of the CuZr 1 /Z, with the activity of CO combustion following the order: CuZr 1 /Z < CuCe 0.25 Zr 0.75 /Z < CuCe 0.5 Zr 0.5 /Z < CuCe 1 /Z < CuCe 0.75 Zr 0.25 Z. After cerium addition, the cerium-zirconium mixed oxides formed promoted the copper species well dispersed on the catalyst surface. The high activities of cerium-containing catalysts were closely related to the synergetic effects among the copper, cerium, and zirconium species, as the surface copper species provided sites for CO adsorption and the cerium-zirconium mixed oxides promote the activation of oxygen. The activities were probably also attributed to some copper species present as substitutional defects in the ceria lattice, which were more reducible than the copper clusters, minicrystals, and bulk CuO particles. The CuCe 0.75 Zr 0.25 /Z possessed excellent redox capacity, adsorption/activation properties for O and CO species, and therefore induced a self-sustained combustion of CO at the lowest temperature than that of other CuCe 1-x Zr x O y /ZSM-5 catalysts.ARTICLE HISTORY

Reaction mechanism and kinetics of CO oxidation over a CuO/Ce0.75Zr0.25O2-δ catalyst

“…Cu(NO 3 ) 2 ·3H 2 O, Ce(NO 3 ) 3 ·6H 2 O and Zr(NO 3 ) 4 ·5H 2 O were combined in a 4:3:1 M ratio and dissolved fully in 70 mL of ethanol at 80°C. This Cu:Ce:Zr ratio was selected on the basis of our previous study according to its good redox capability and oxygen storage capacity for CO oxidation [22,23]. Then, 0.24 mol/L of an oxalic acid solution was used as a pore former and was added quickly to the aforementioned nitrate solution with stirring to evaporate ethanol and to fully dissolve until a gel was formed at 80°C over nearly 6 h. After aging at room temperature for approximately 48 h, the gel was dried at 105°C for 12 h and then calcined in air at 550°C for 2 h.…”

Plasma-catalytic oxidation of toluene over MCeZrOx/TiO2 (M = Cu, Mn, Ni and Co) catalysts using a dielectric barrier discharge reactor

“…This molar ratio was determined based on our previous study where we found that this ratio can form a M-cerium synergy and a cerium-zirconium solid solution, which improved the redox capability and oxygen storage capacity of the catalysts. 28 The resulting solution was stirred at 80 °C with a pH of ∼7.0 for 24 h. Subsequently, the samples were dried and then calcined at 550 °C for 4 h, pressed and sieved to 20–40 mesh. The chemical composition of the catalysts was measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) to confirm the M/Ce/Zr molar ratio of the catalysts.…”

Critical Review of Low-Temperature CO Oxidation and Hysteresis Phenomenon on Heterogeneous Catalysts

“…Simultaneous oxidation of CO and CH 4 on Pt/Al 2 O 3 and Pt/CeO 2 results in a reverse hysteresis for methane oxidation [5]. Moreover, CO self-sustained combustion over the Cu-Ce/ZSM-5 or CuCe 1-x Zr x O y /ZSM-5 catalyst has been reported [91,92]. The explanation of hysteresis effects by multiple steady states has been comprehensively reviewed by Hlaváček et al [93].…”

“…Increasing CO concentration in inlet gas causes a higher light-off temperature or ignition point, the hysteresis loop increases upon increasing the CO concentrations [52,56,74,77,87,126,142] Inlet Temperature Ignition and extinction shifted to higher temperatures with rapid increase in CO conversion [77,[128][129][130][131][132][133][134] Surface Contamination and Aging Increase in the hysteresis width due to the removal of contamination that blocks active sites [75,94,141] [55, 94,140] Rate of temperature ramp-up Increase in the temperature ramp-up result in shifting the ignition curve to higher temperatures [72,92] Inhibition parameters Different inhibiting species accumulation on catalyst surface can change the shape of hysteresis curves and increase the width of the hysteresis. [141,142].…”