Catalytic ignition of CO over CuCeZr based catalysts: New insights into the support effects and reaction pathways

Self-sustained catalytic combustion is a promising strategy to remove CO from the off-gas produced during steelmaking, where the potential catalysts are bulk copper-cerium-zirconium mixed oxides or those supported on TiO2 or ZSM-5 substrates. In this study, the effects of the catalyst support on the CO catalytic ignition perfor-mance and reaction pathways were investigated by FTIR coupled with a novel in-situ cell, together with the state-of-the-art characterization techniques. The Infrared (IR) transmission cell equipped with a magnetically driven system, could effectively prevent overlaps between active intermediate peaks (Cu+-CO and Cu+(CO)2) and gaseous CO peaks. The Cu+ cations located at the phase interface are the main active sites. The Cu and Ce in-teractions lead to the formation of solid solutions of CuCe0.75Zr0.25O8 (CuCeZr). The monocarbonyls [Cu+-CO1 are the dominant species during CO oxidation, and the vacancies in the solid solutions are occupied by oxygen, accelerating the oxygen cycle. The TiO2 or ZSM-5 supports promote copper dispersion over CuCe0.75Zr0.25O8/ TiO2 (CuCeZr/T) and CuCe0.75Zr0.25O8/ZSM-5 (CuCeZr/Z) catalysts, which can be attributed to their high surface areas (168.2 and 346.3 m2/g, respectively), while the Cu-Ce interactions are less relevant. Hence, CO oxidation mainly occurs at the phase interface between copper oxide and TiO2/ZSM-5. Dicarbonyls [Cu+(CO)21 are the main intermediates for the CuCeZr/T and CuCeZr/Z catalysts, and the Cu2+ species are reduced to form dicar-bonyls that also take part in the oxidation process. Although a well copper dispersion enhances the activity of individual copper sites on the CuCeZr/T and CuCeZr/Z catalysts, considering the redshift of the carbonyl bands and the increase in CO adsorption, the close interactions and high contents of Cu and Ce favor the local accu-mulation of heat and mass transfer over bulk CuCeZr, leading to the ignition of CO at low temperatures.

Automated summary

The effects of catalyst support on the CO catalytic ignition performance and reaction pathways were investigated, and it was found that TiO2 or ZSM-5 supports promote copper dispersion and the oxidation process mainly occurs at the phase interface. The Cu and Ce interactions lead to the formation of solid solutions, which enhance the activity of individual copper sites and favor the ignition of CO at low temperatures. The Cu2+ species are reduced to form dicarbonyls, which also take part in the oxidation process.