Alkylation of benzene with carbon dioxide to low-carbon aromatic hydrocarbons over bifunctional Zn-Ti/HZSM-5 catalyst

Alkylation of benzene to value-added, high octane number and low toxic toluene and xylenes provides a way to lower benzene content in gasoline pool, and is hence a method to promote fuel quality. On the other hand, CO₂ accumulation in the atmosphere causes global warming and requires effective route for its valorization. Utilization of CO₂ as a carbon source for benzene alkylation could achieve both goals. Herein, alkylation of benzene with CO₂ and H₂ was realized by a series of low-cost bifunctional catalysts containing zinc/titanium oxides (Zn/Ti oxides) and HZSM-5 molecular sieves in a fixed-bed reactor. By regulating and controlling oxygen vacancies of Zn/Ti oxides and the acidities of HZSM-5, benzene conversion and CO₂ conversion reached 28.7% and 29.9% respectively, along with a total selectivity of toluene and xylene higher than 90%. In this process, more than 25% CO₂ was effectively utilized and incorporated into the target products. Moreover, the mechanism of the reaction was analyzed and the course was simultaneously traced. CO₂ was transformed into methanol firstly, and then methanol reacted with benzene generating toluene and xylene. The innovation provides a new method for upgrading of fuels and upcycling the emissions of CO₂, which is of great environmental and economic benefits.