E. A. Redekop

Acidity effect on benzene methylation kinetics over substituted H-MeAlPO-5 catalysts

M. Morten, T. Cordero-Lanzac, P. Cnudde, E. A. Redekop, S. Svelle, V. Van Speybroeck, U. Olsbye

Journal of Catalysis

404, 594-606

2021

A1

Abstract

Methylation of aromatic compounds is a key reaction step in various industrial processes such as the aromatic cycle of methanol-to-hydrocarbons chemistry. The study of isolated methylation reactions and of the influence of catalyst acidity on their kinetics is a challenging task. Herein, we have studied unidirectional metal-substituted H-MeAlPO-5 materials to evaluate the effect of acid strength on the kinetics of benzene methylation with DME. First-principle simulations showed a direct correlation between the methylation barrier and acid site strength, which depends on the metal substituent. Three H-MeAlPO-5 catalysts with high (Me = Mg), moderate (Me = Si) and low acidity (Me = Zr) were experimentally tested, confirming a linear relationship between the methylation activation energy and acid strength. The effects of temperature and reactant partial pressure were evaluated, showing significant differences in the byproduct distribution between H-MgAlPO-5 and H-SAPO-5. Comparison with propene methylation suggested that the Mg substituted catalyst is also the most active for the selective methylation of alkenes.

Open Access version available at UGent repository

Gold Open Access

DOI

http://dx.doi.org/10.1016/j.jcat.2021.11.002

Experimental and theoretical evidence for promotional effect of acid sites on the diffusion of alkenes through small-pore zeolites

P. Cnudde, E. A. Redekop, W. Dai, N.G. Porcaro, M. Waroquier, S. Bordiga, M. Hunger, L. Li, U. Olsbye, V. Van Speybroeck

Angewandte Chemie int. Ed.

60(18): 10016-10022

2021

A1

Abstract

The diffusion of saturated and unsaturated hydrocarbons is of fundamental importance for many zeolite‐catalyzed processes. Transport of small alkenes in the confined pores of narrow pore zeolites can become hindered, resulting in a significant impact on the ultimate product selectivity and separation. Herein, intracrystalline light olefin/paraffin diffusion through the 8‐ring windows of zeolite SAPO‐34 is characterized by a complementary set of first‐principle molecular dynamics simulations, PFG‐NMR experiments and pulse‐response Temporal Analysis of Products measurements, yielding information at different length and time scales. Our results clearly show a promotional effect of the presence of Brønsted acid sites on the diffusion rate of ethene and propene, whereas transport of alkanes is found to be insensitive to the presence of acid sites. The enhanced diffusivity of unsaturated hydrocarbons is ascribed to the formation of favorable π‐H interactions with acid protons, as confirmed by IR spectroscopy measurements. The acid site distribution is proven to be an important design parameter for optimizing product distributions and separations.