Template-assisted preparation of metal-modified SAPO-34 molecular sieves for the catalysis of methanol-to-olefins

To improve the dispersion of metals and to enhance the catalytic performance of SAPO-34 molecular sieves, the template-assisted method was applied to synthesize Co, Ni and Zn modified SAPO-34 molecular sieves by using palygorskite as silicon source and tetraethylammonium hydroxide as template. The metal modified SAPO-34 molecular sieves were characterized by XRD, SEM, XPS, N-2-adsorption-desorption, NH3-TPD, FTIR, ICP-AES and TG. The N atoms of tetraethylammonium hydroxide exhibited the different forces to three metal ions, thus the acidity of the molecular sieves was further regulated. Compared with metal modified SAPO-34 molecular sieves prepared by impregnation, metal modified SAPO-34 molecular sieves prepared by template-assisted maintained higher surface area, bigger pore volume and better dispersion of metals. The catalytic performance of metal modified SAPO-34 molecular sieves prepared by template-assisted method in the reaction of methanol-to-olefins (MTO) was investigated in the fixed bed reactor. Under the reaction conditions that the reaction temperature was 400 degrees C, the reaction pressure was 0.1 MPa, the feed WHSV was 2.0 h(-1) and the mass of catalyst was 0.5 g, Ni modified SAPO-34 molecular sieves exhibited great methanol conversion and high selectivity to light olefins. The selectivity of light olefins reached 95.7%.

Automated summary

The study successfully synthesized metal-modified SAPO-34 molecular sieves using the template-assisted method, which exhibited better dispersion and catalytic performance compared to those prepared by impregnation. Ni-modified SAPO-34 molecular sieves showed high methanol conversion and selectivity to light olefins in the methanol-to-olefins reaction.