Zn-promoted hydrogen exchange for methane and ethane on Zn/H-BEA zeolite: In situ 1H MAS NMR kinetic study

Significant Influence of Zn on Activation of the C‐H Bonds of Small Alkanes by Brønsted Acid Sites of Zeolite

“…The parent samples contained no extra-framework aluminium, but a small quantity of extraframework aluminium (< 2 %) was created during the sample activation procedure as was confirmed by 1 H and 27 Al MAS NMR. [37] XRD analysis indicated the presence of bulk ZnO in the Zn-modified zeolites and SEM confirmed the presence of ZnO as clusters of 50-100 nm on the surface of crystallites of both zeolites. UV/Vis diffuse reflectance spectra of Zn/H-BEA and Zn/H-ZSM-5 have shown the presence of sub-nanometric ZnO clusters and macrocrystalline particles of ZnO on the extra surface of the zeolite, exhibiting bands at 265 and 370 nm, respectively.…”

“…[28,36,37] This allows us to clarify important mechanistic details of alkane activation by Brønsted acid sites upon modification of the zeolites by Zn.…”

“…Detailed characteristics of the zeolite catalysts used are provided elsewhere. [37,46] Perdeuterated C 1 -n-C 4 alkanes (99 % D) purchased from Aldrich Chemical Company Inc. C 1 -C 3 were used without further purification, whereas n-C 4 was additionally purified from admixed olefins by several cycles of adsorption-desorption on zeolite mordenite (H-MOR) at 373 K. The samples for NMR measurements were prepared by heating 80 mg of the zeolite sample in the glass tubes of 5.5 mm outer diameter. The samples were activated by an increase of the temperature from 300 to 673 K at the rate of 10 K h À1 under vacuum.…”

Low‐Temperature Alkane CH Bond Activation by Zeolites: An In Situ Solid‐State NMR H/D Exchange Study for a Carbenium Concerto

“…These values are close to the H/D exchange reaction between the isobutane molecule on the methyl position and H-ZSM5 (50 kJ mol À1 ), [13,36] much closer than to the value for the methane and H-Beta reaction (138 kJ mol À1 ). [37] The difference of 88 kJ mol À1 between methane and isobutane has been imputed to the difference in chemical pathways with these respective molecules for which the former favors carbonium chemistry and the latter carbenium chemistry.…”

Recent development in in situ NMR study on heterogeneous catalysis: mechanisms of light alkane functionalisation

“…Therefore, Stepanov et al carried out in situ 1 H MAS NMR kinetic study on hydrogen exchange between light alkanes (methane and ethane) and Brønsted acid sites of both H-BEA and Zn-loaded Zn/H-BEA. 40 Fig . 4 shows the 1 H MAS NMR spectra of CD 4 adsorbed on H-BEA.…”