Tuning zeolite crystal size in bifunctional catalysts assembled on bio-SiO2 for enhanced CO2 hydrogenation to light olefins

CO 2 hydrogenation to high-value-added light olefins over bifunctional catalysts is a promising pathway toward achieving net zero emissions. Herein, a series of SAPO-34 zeolites (bio-SAPO-34) with consistent acid properties but different particle sizes ( e.g. , 170 nm, 610 nm, and 7.50 μm) were synthesized using rice husk as the sole silicon source. Meanwhile, the rice husk derived SiO 2 (bio-SiO 2 ) could serve as a platform to assemble SAPO-34 and ZnZrO x into a bifunctional catalyst. It was found that the bio-SAPO-34 with the smaller particle size resulted in higher selectivity of light olefins and better long-term stability. Especially, after integration with ZnZrO x , the bio-SAPO-34 with a particle size of 170 nm exhibited higher light olefins selectivity (89.6 vs. 58.5 %) and longer catalytic lifetime (1000 vs. 59 min), as compared to a particle size of 26.0 μm. Notably, the zero length column (ZLC) technique, N 2 physisorption, and thermogravimetric analyses revealed that reducing the particle size of bio-SAPO-34 significantly decreases the diffusion resistance of light olefins in zeolites by shortening the diffusion paths, thereby inhibiting the formation of coke and enhancing the catalytic stability. Moreover, the bio-SiO 2 platform acts as a light olefins diffusion promoter by decreasing the surface diffusion resistance between zeolite particles and significantly alleviating the coke formation.