Coupling dry reforming of methane with in-situ catalytic cracking of coal pyrolysis tar over xNi@HZSM-5

Abstract

An in-situ upgrading process of gaseous tar based on catalytic cracking of coal pyrolysis tar combining with dry reforming of methane (DRM) over xNi@HZSM-5 was proposed. The results show that light tar content over 2Ni@HZSM-5 is 80 wt% at 600 °C, and light tar yield raises from 6.0 wt% to 8.1 wt%. Compared with the Ni-based catalyst prepared by impregnation, 2Ni@HZSM-5 can separate active sites of DRM and tar cracking via the confinement effect of zeolite, so that CH₄ conversion activity and tar cracking activity are individually regulated, and excessive cracking of tar by Ni can be avoided. Highly dispersed Ni particles in HZSM-5 pores promote the conversion of CH₄, and the stabilization effect of hydrogen-rich free radicals on tar cracking fragments is strengthened. After the catalytic upgrading process over 2Ni@HZSM-5, the average molecular weight of tar drops down to 223 amu. Through isotope tracing experiments, it was confirmed that the active centers of tar cracking and CH₄ activation during the upgrading process are acid sites of HZSM-5 and Ni respectively. Aromatic hydrocarbons with 3 and 4 rings are converted by 2Ni@HZSM-5, and the cracking fragments are combined with ·H and ·CH_x to form monocyclic and bicyclic aromatic hydrocarbons.