Insights into the Active Species of Nanoparticle‐Functionalized Hierarchical Zeolites in Alkylation Reactions

Abstract

Supported iron oxide nanoparticles have been incorporated onto hierarchical zeolites by microwave‐assisted impregnation and mechanochemical grinding. Nanoparticle‐functionalised porous zeolites were characterised by a number of analytical techniques such as XRD, N2 physisorption, TEM, and surface acidity measurements. The catalytic activities of the synthesised nanomaterials were investigated in an alkylation reaction. The results pointed to different species with varying acidity and accessibility in the materials, which provided essentially different catalytic activities in the alkylation of toluene with benzyl chloride under microwave irradiation, selected as the test reaction.

Hierarchical Zeolites and their Catalytic Performance in Selective Oxidative Processes

“…All hierarchical ZSM-5 zeolites exhibited type I + IV isotherms typical of micro-and mesoporous materials, as compared to the type I isotherms observed for parent microporous zeolites (Z40c and Z15c). [33] The surface areas of Z40c-H and Z15c-H, particularly the "external" surface area, were comparably superior to those of the parent microporous materials after the introduction of mesoporosity, Table 1 (see Ref. [33] for further details).…”

“…[33] The surface areas of Z40c-H and Z15c-H, particularly the "external" surface area, were comparably superior to those of the parent microporous materials after the introduction of mesoporosity, Table 1 (see Ref. [33] for further details).…”

“…The surface acid properties of these catalysts were investigated and correlated to the catalytic activity of these materials in the microwave-assisted alkylation of toluene with benzyl chloride, preferentially catalyzed by Lewis acids. [33] In light of these findings, we set out to investigate the feasibility of using these hierarchical zeolites, with and without iron oxide nanoparticles, in selective oxidation processes taking advantage of terminal AlÀOH groups to generate redox sites in zeolites. Mesoporous ZSM-5 materials were consequently synthesized and employed in various selective oxidation test reactions under microwave irradiation, namely the oxidation of benzyl alcohol to benzaldehyde, the epoxidation of cyclohexene, and the multistep conversion of N,N-dimethyl formamide (DMF) into products of interest.…”

“…Moreover these two bases, with differing molecular dimensions, may detect acid sites located in different pore spaces, that is, PY reaches all acid sites either in micropores or in mesopores/on the surface, while DMPY is only applicable the quantification of acid sites in mesopores or on the surface. [24,33,34] Therefore, the development of mesoporosity in Z40c-H and Z15c-H samples is related to the higher accessibility of DMPY, giving rise to a materials with essentially B acid sites, as shown in Table 1. [33] Base titration experiments correlated well with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of PY adsorbed on zeolites ( Figure 1 and Supporting Information).…”

“…[24,33,34] Therefore, the development of mesoporosity in Z40c-H and Z15c-H samples is related to the higher accessibility of DMPY, giving rise to a materials with essentially B acid sites, as shown in Table 1. [33] Base titration experiments correlated well with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of PY adsorbed on zeolites ( Figure 1 and Supporting Information). Z15c-H and Z40c-H generally exhibited a much lower concentration of accessible Lewis acid sites as compared to their parent microporous counterparts, both systems having a large concentration of Brønsted acid sites developed upon HCl treatment (particularly Z15 materials, Figure 1).…”