Oxidative Benzene Methylation with Methane over MCM-41 and Zeolite Catalysts:  Effect of Framework Aluminum, SiO₂/Al₂O₃ Ratio, and Zeolite Pore Structure

Abstract

The effect of framework aluminum, SiO 2 /Al 2 O 3 ratio, and zeolite pore structures on the oxidative methylation of benzene with methane in a high-pressure batch reactor have been studied using a range of MCM-41 samples and zeolites as catalysts. The presence of framework aluminum in MCM-41 has been shown to be important for providing the required Bro ¨nsted acid sites for the reaction. Among the catalysts tested, HZSM-5, CoZSM-5, and H-beta were found to exhibit the best performance, while mordenite was found to be virtually inactive for the reaction. HY and NaY exhibited intermediate performance, but HY, due to its higher acidity, was more active than NaY. H-beta, being more acidic, showed slightly higher activity than the ZSM-5 catalysts due to extra contribution to methylated products formation by cracking of benzene without participation of methane. Differences in the catalytic activities and product selectivities of these catalysts have also been discussed in terms of the variations in the number of available Bro ¨nsted acid sites, SiO 2 /Al 2 O 3 ratios, and zeolite pore structures.

Advanced Catalysts Based on Micro‐ and Mesoporous Molecular Sieves for the Conversion of Natural Gas to Fuels and Chemicals

“…Several protic and metal exchanged zeolites as well as ordered mesoporous silicates have been tested in the high-pressure oxidative alkylation of benzene and toluene with methane [18][19][20]. Regarding benzene, it has been shown that molecular sieves bearing acidic sites of moderate strength are responsible for the alkylation step, employing the endo-generated methanol as alkylating agent.…”

“…By contrast, when strong acidity is brought into play, as in the case of H-beta zeolite, an alternative reaction pathway is able to operate by using fragments derived from the cracking of benzene as alkylating agents, and, in this case, the reaction can proceed in the absence of oxygen [17]. The need for a moderate acidity is appraised from the results from Adebajo et al [19,20] in the alkylation of benzene with CH 4 at a pressure of 6.9 MPa and a temperature of 400 • C in a batch reactor. Thus, as shown in Table 21.1, MCM-41 mesoporous silica in its pure silica form or containing Cu do not hold acid sites with the required strength as to catalyze the reaction, while this mesoporous molecular sieve becomes active when it is synthesized as an aluminosilicate, owing to the presence of Brønsted acid sites.…”

“…e Si/Al = 56. Reaction conditions: T = 400 • C, P = 6.9 MPa, CP-grade methane, reaction time = 4 hours, reactants loaded with no removal of residual oxygen[19,20].…”

Alkylation of Benzene with Methane over ZnZSM-5 Zeolites Studied with Solid-State NMR Spectroscopy

“…demonstrated that addition of molecular oxygen facilitated activation of methane in the coconversion of methane and propane over Ga/beta zeolite . Moreover, for the reaction of methane and benzene, other researchers proposed that the molecular oxygen had a remarkable enhancement on the formation of methylated aromatic products over various zeolites. − …”