Effective conversion of CO2 into light olefins over a bifunctional catalyst consisting of La-modified ZnZrOx oxide and acidic zeolite

Abstract

Effectively promoting the formation of methanol intermediates is the key to improve the catalytic performance of a bifunctional catalyst in CO₂ hydrogenation to light olefins. Herein, a series of lanthanum (La) modified zinc–zirconium oxides (ZnZrO_x(nLa)) were prepared by a one-pot sol–gel method with glucose as the complexing agent. The results indicate that ZnZrO_x(nLa) gives higher methanol selectivity and CO₂ conversion than those on ZnZrO_x in CO₂ hydrogenation. XRD, Raman, N₂ sorption, TEM/HRTEM, XPS, CO₂/H₂-TPD and in situ DRIFT spectroscopy measurements confirm that the addition of an appropriate amount of La can induce the formation of more oxygen vacancies on the surface of ZnZrO_x, hence promoting the adsorption and activation of CO₂, as well as the generation of more formate and methoxy intermediates. Upon coupling with acidic zeolites, the methanol intermediates generated on ZnZrO_x(nLa) are rapidly converted into light olefins over the acid sites. As a result, ZnZrO_x(0.3La)/H-SAPO-34 and ZnZrO_x(0.3La)/H-SAPO-18 composite catalysts show a C₂⁼–C₄⁼ selectivity in hydrocarbons as high as 83.2% and 77.5%, respectively, despite their light olefin distribution being different, due to the variation of the acid strength and strong acid content between H-SAPO-34 and H-SAPO-18.