•Monolayer of silica on well-shaped one-dimensional γ-Al2O3 is obtained.•Moderate aggregated MoOx on silica deposited one-dimensional γ-Al2O3.•Highly catalytic performance of the Mo species in moderate aggregation.•A formation rate of 38.9 × 10−9 mol m−2 s−1 for 1-butene metathesis to propene.1-Butene, abundant but inexpensive in industry, can be used to produce more valuable propene and ethene through the well-known metathesis reaction. In terms of catalyst system of molybdena, controlling the interaction between the molybdena and the support is quite crucial. A special support, i.e., well-shaped one-dimensional γ-Al2O3 with uniform diameters of ∼10 nm and lengths of ∼100 nm, has been synthesized via oleylamine-assisted hydrothermal method. The molybdenum oxides are well controlled in sizes of moderate aggregation suitable for 1-butene metathesis with a fairly high rate of propene production (38.9 × 10−9 mol m−2 s−1, 30 mol% yield in a single pass) under mild conditions. The status of MoOx species in the catalyst has been investigated by solid state 29Si MAS NMR, Raman, UV–vis, H2-TPR and NH3-TPD techniques. The catalyst, highly stable after twelve times of regeneration, is important for practical utilization for the metathesis reactions.

The conversion of sugars to chemicals in aqueous-phase is especially important for the utilization of biomass. In current work, zirconium phosphate obtained by hydrothermal methods using organic amines as templates has been examined as a solid catalyst for the dehydration reaction of xylose to furfural in aqueous-phase. The use of dodecylamine and hexadecylamine in the synthesis process results in mesoporous zirconium phosphate with uniform pore width of ∼2 nm and in morphology of nanoaggregates, which is characterized by powder X-ray diffraction, N2 isothermal sorption, NH3 temperature-programmed desorption, FT-IR, and 31P MAS NMR spectroscopy. When used as a catalyst for xylose dehydration to furfural in aqueous-phase, the mesoporous zirconium phosphate presents excellent catalytic performance with high conversions up to 96% and high furfural yields up to 52% in a short time of reaction. Moreover, the catalyst is easily regenerated by thermal treatment in air and shows quite stable activity. The open structure with numerous active sites of the Brønsted/Lewis acid sites is responsible for the high catalytic efficiency of mesoporous zirconium phosphate.

•Space proximities of acid sites are predominant in HZSM-5 with low Si/Al ratio.•Reactant molecule suffers increased positive charge from multi Brønsted acid sites.•Fructose dehydration is accelerated by cooperative catalysis of adjacent acid sites.•The measured activation energies decrease with increased adjacent acid sites.5-Hydroxymethylfurfural (HMF) is an important platform chemical that can be obtained from biomass by acid catalysis. In the current investigation, an acceleration of the dehydration of fructose to HMF with an increased reaction rate and decreased activation energy is identified over the adjacent acid sites in MFI-type zeolites. The spatial proximities of these sites become prominent with the decrease of the Si/Al ratio in HZSM-5 and increase the charge density on the adsorbed reactant molecule according to 13C MAS NMR results. The cooperative catalysis by the adjacent acid sites is deduced and it is very important to develop new effective acid catalysts.Download high-res image (122KB)Download full-size image

•The spatial proximity between BAS is demonstrated in MFI zeolites.•The adjacent BAS cooperatively catalyze alkane cracking at higher cracking rates.•Adsorption entropies are more negative for alkane on two adjacent BAS.•More positive intrinsic activation entropy on two adjacent BAS leads to this enhancement.The spatial proximity between Brønsted acid sites (BAS) in HZSM-5 zeolites is demonstrated by 1H double quantum (DQ) MAS NMR measurements. This proximity results in more pronounced polarization of adsorbed acetone and alkanes in zeolites, evident from 13C MAS NMR spectra. The adjacent BAS with synergistic interactions on alkane reactants (propane, n-butane, and n-pentane) cooperatively catalyze alkane cracking at higher turnover rates than on isolated BAS. Apparent activation energies are similar on HZSM-5 catalysts with different concentrations of isolated and adjacent BAS, while apparent activation entropies become less negative at higher BAS concentrations. Kinetic experiments in conjunction with adsorption measurement and DFT calculations prove that cracking rates at these Al-site pairs are mainly due to more positive intrinsic activation entropies, suggesting that the protonation transition state occurs later along the reaction coordinate on adjacent BAS. Adjacent Brønsted acid sites favor cracking over dehydrogenation and favor central cracking over terminal cracking.Download high-res image (196KB)Download full-size image