posted on 2024-03-11, 13:03authored byYilun Ding, Yongzhi Zhao, Dengyun Miao, Zhili Wang, Jingyao Feng, Feng Jiao, Xiulian Pan, Xinhe Bao
MWW zeolites are widely used heterogeneous catalysts,
which have
two-dimensional 10-membered ring (10MR) sinusoidal channels and 12MR
supercages connected by 10MR openings. We study herein the Al distribution
and its correlation with the catalytic performance by taking MCM-22
and MCM-49 as models since they exhibit the same three-dimensional
MWW structure and can be prepared with different ratios of organic
template to inorganic cations. 27Al MAS NMR, 29Si MAS NMR, and infrared (IR) spectroscopy show that HMCM-22 has
more Al atoms at the T7 sites, which generate more Bro̷nsted
acid sites in the sinusoidal channels, while HMCM-49 has more Bro̷nsted
acid sites in the supercages. As a result, HMCM-49 in combination
with ZnCrOx oxide (ZnCrOx-HMCM-49) as a composite catalyst exhibits a longer induction
period than ZnCrOx-HMCM-22 in syngas conversion
to gasoline range hydrocarbons. It needs more than 120 h to reach
a stable gasoline selectivity for ZnCrOx-HMCM-49. In contrast, it reduces to less than 20 h over ZnCrOx-HMCM-22. This could be attributed to the
narrow opening between supercages which limits the diffusion of hydrocarbons
generated in the supercages and hence accumulation to form carbon
deposits.