Mesoporous Beta Zeolite Catalysts for Benzylation of Naphthalene: Effect of Pore Structure and Acidity

Abstract

To improve the catalytic performance of zeolite catalysts in reactions involving bulky molecules, a series of mesoporous Beta zeolite were prepared using organic functionalized fumed silica as the silicon source, which were thoroughly characterized in terms of porosity and acidity. The peaks in X-ray diffraction (XRD) patterns showed broadening, and the external surface area and mesoporosity increased progressively when the content of organic functionalization increased. An infrared (IR) spectroscopy study of adsorbed probe molecules, including pyridine (Py-IR), 2,6-ditertbutylpyridine (DTBPy-IR) and pivalonitrile (Pn-IR), showed that the improvement of mesoporosity increased the accessibility of acidic sites. In the catalytic benzylation of naphthalene with benzyl chloride (BC) over the mesoporous Beta zeolite catalysts, the conversion of BC was significantly increased when the accessibility of Brönsted acid sites improved. The increase of mesoporosity not only improved the diffusion ability of the reactants and products, but also increased the accessibility of acid sites, which greatly enhanced the activity of the mesoporous Beta zeolite catalysts. It is highlighted that the interdependence of mesoporosity, acid type, acid concentration, and strength of the mesoporous Beta zeolites on the catalytic performance in the benzylation of naphthalene with BC was comprehensively studied.

The Steric Effect in Green Benzylation of Arenes with Benzyl Alcohol Catalyzed by Hierarchical H-beta Zeolite

“…To obtain more detailed information about Brönsted acid sites (BAS) and Lewis acid sites (LAS), the amount of weak acid sites from NH3-TPD results was used to represent amount of LAS, while the amount of strong acid sites from NH3-TPD results was used to represent amount of BAS [36,37]. A correlation of catalytic activity with the amount of BAS and LAS was built in Figure 4b, from which we can see in general that in the probe benzylation of p-xylene in 373K, three hierarchical beta zeolites Hβ-4, Hβ-2 and Hβ-3 show rising activity as the BAS and LAS amount increase, in consistent with previous studies in catalytic benzylation [5,7,28]. However, microporous Hβ-1 is superior in BAS and LAS amount but has the lowest activity, and we infer the less external surface area of Hβ-1 (Table 1) was to blame.…”

“…According to their view, small base probe molecules like NH 3 and pyridine fail to access the external surface, which is available for large reactant molecule. Hao et al [7] also found the accessibility of BAS is critical to the activity and both BAS and LAS have positive correlation with catalytic activity in benzylation of naphthalene. To sum up, combine acidity and porosity, containing more abundant acid sites amount than Hβ-2 and Hβ-4, and larger external surface area than microporous Hβ-1, no wonder Hβ-3 shows the best performance.…”

“…However, microporous Hβ-1 is superior in BAS and LAS amount but has the lowest activity, and we infer the less external surface area of Hβ-1 (Table 1) was to blame. It is already known that porosity and acidity both affect the catalytic performance in benzylation reactions with zeolite catalysts [7,11,28]. Wang et al [28] studied the difference of parent beta zeolite and mesoporous zeolite made from post treatment method in catalyzing benzylation of benzene and mysitylene.…”

“…Compared to BzCl, which produces HCl as a by-product and, often causes corrosion and catalyst leaching problems, BzOH is an environmentally friendly benzyl reagent, whose main by-product besides benzylation is only water. However, in the research for better reactivity and no etherification to form dibenzyl ether (DBE), to decrease selectivity [5], extensive works have already been published using BzCl [6][7][8][9][10][11]. It is still necessary to gain more insight on understanding catalytic reaction mechanisms with the more challenging BzOH as benzyl reagent because as one of the enduring research themes in chemistry [12][13][14][15][16][17][18], developing green catalytic process is beneficial to build an ecofriendly and sustainable economy.…”

In situ Generated Ru(0)-HRO@Na-β From Hydrous Ruthenium Oxide (HRO)/Na-β: An Energy-Efficient Catalyst for Selective Hydrogenation of Sugars

“…Figure 8). Some of the finer Ru particles deposit on the pores (0.67 nm) of β-zeolite support (Hao et al, 2018). The Stokes diameter of xylose is 0.64 nm, which can easily enter β-zeolite pores and interact with the ultrafine Ru particles.…”