Cerium-induced modification of acid-base sites in Ni-zeolite catalysts for improved dry reforming of methane

Abstract

Dry reforming of methane (DRM) is a promising route to mitigate greenhouse gas emissions by converting CH₄ and CO₂ into valuable syngas. The present work explores the effect of Ce addition to Ni-based catalysts supported on CBV3020E (ZSM-5) for DRM. The use of Ce as a promoter to tune the acid-base properties of zeolites for DRM is addressed for the first time in detail. While Ce has traditionally been used to improve oxygen storage capacity, this work explores its novel use as a means to enhance surface basicity and promote CO₂ adsorption. The samples were prepared by wet impregnation, characterized using N₂-sorption, X-ray diffraction, H₂-temperature-programmed reduction, temperature-programmed desorption of CO₂ and ammonia, and Fourier transforms infrared spectroscopy, and tested for DRM at 800 °C and 42,000 mL/g.h GHSV. Results show that ZSM-5 zeolite can be beneficial in achieving high metal dispersion. The introduction of 2 wt% Ce to Ni₅/ZSM-5 increases the concentration of strong basic sites, resulting in improved catalytic performance from 37 % CH₄ conversion and 48 % CO₂ conversion for Ni₅/ZSM-5 to 55 % and 65 % on promoted Ni₅Ce₂/ZSM-5, respectively. Thus, the best results are observed on Ni₅Ce₂/ZSM-5 and an optimal H₂/CO ratio of 0.84 is achieved in this case. Upon decreasing GHSV to 15,000 mL/g.h, CH₄ and CO₂ conversions jump to 83 % and 88 %, respectively on Ni₅Ce₂/ZSM-5. Cerium doping produces more desirable strong basic sites and enhances NiO reducibility. This promotes CO₂ adsorption and drives the catalytic reaction towards syngas formation, which eventually results in increased efficiency and improved performance.