In-depth investigating of the Initiation Sites and Steps of Carbon Deposition on CeY Zeolites in FCC Hydrogen Transfer Reactions

Abstract

Rare-earth Y zeolite (REY) is crucial in the FCC process for cracking heavy oil molecules into gasoline and diesel. However, REY zeolites tend to deactivate from carbon deposition during use. Currently, elucidating the carbon footprint on rare-earth modified zeolites during FCC reactions and establishing the relationship between acidity and carbon deposition selectivity at active sites remain significant challenges. In this study, cyclohexene was employed as a model probe to investigate the acidic sites of REY zeolites and the initial stages of carbon deposition through XRD with the Rietveld refinement, in-situ infrared adsorption, catalytic conversion experiments, and microscopic hydrogen transfer reaction activity tests. The experimental results demonstrated that by precisely controlling the Ce loading and its distribution within the Y-type zeolite framework, the sites containing active hydroxyl groups (O (2)H/O (1)H) and the acidity of the catalyst could be effectively modulated. This modulation enabled micro-scale control over the hydrogen transfer reaction pathways, inhibited excessive hydrogen transfer reaction, intercepted the initiation steps of carbon deposition, altered the carbon footprint and consequently influenced the selectivity of carbon deposition.Based on these findings, a dynamic equilibrium was identified between hydroxyl-based active centers in Ce-NaY zeolites and the competing processes of carbon formation and removal. This provided crucial experimental evidence for the efficient and selective synthesis of target products using REY zeolite catalysts in catalytic cracking reactions.