Nianhua Xue

High performance mesoporous zirconium phosphate for dehydration of xylose to furfural in aqueous-phase

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 Bronsted/Lewis acid sites is responsible for the high catalytic efficiency of mesoporous zirconium phosphate.

The Key Points of Highly Stable Catalysts for Methane Reforming with Carbon Dioxide

Stable catalysis performance in long‐term operation is crucial for the wide‐scale industrialization of catalytic processes. The degradation of catalysts is a considerable problem for methane reforming with carbon dioxide, owing to carbon deposition on active sites and/or catalytic supports, and sintering of active components at high temperatures. With base metals and a modified alumina support, the present work has developed highly stable catalysts that operate free of coke formation and sintering of active components. Firstly, homogeneous copper‐nickel alloy nanoparticles (NPs), which have never previously been used for this purpose, were produced and then supported as catalytic centers onto alumina. The CuNi alloy catalyst with a Ni to Cu ratio of unity totally prohibits carbon deposition on active centers, while maintaining high activity for the reforming reaction. Second, the modification of alumina by coating with zirconia before supporting the CuNi alloy, drastically inhibits coke formation on the support, prevents the reaction of Cu in the alloy with alumina at high temperatures, and, therefore, promotes the stability of active alloy NPs. Additionally, after supporting the CuNi alloy NPs on zirconia‐coated alumina, the catalyst was coated with a thinner layer of zirconia to protect the CuNi NPs from sintering, while maintaining high activity. This state‐of‐the‐art catalyst is shown to be highly stable for methane reforming with carbon dioxide at high temperatures and the deactivation constant is calculated to be close to zero in a long‐term operation, even at extremely high space velocity of 120 000 mL g−1 h−1. The results are practically important to develop robust, as well as high performance, catalysts for the relevant reactions.

Identification of different oxygen species in oxide nanostructures with 17O solid-state NMR spectroscopy

Nanostructured oxides find multiple uses in a diverse range of applications including catalysis, energy storage, and environmental management, their higher surface areas, and, in some cases, electronic properties resulting in different physical properties from their bulk counterparts. Developing structure-property relations for these materials requires a determination of surface and subsurface structure. Although microscopy plays a critical role owing to the fact that the volumes sampled by such techniques may not be representative of the whole sample, complementary characterization methods are urgently required. We develop a simple nuclear magnetic resonance (NMR) strategy to detect the first few layers of a nanomaterial, demonstrating the approach with technologically relevant ceria nanoparticles. We show that the 17O resonances arising from the first to third surface layer oxygen ions, hydroxyl sites, and oxygen species near vacancies can be distinguished from the oxygen ions in the bulk, with higher-frequency 17O chemical shifts being observed for the lower coordinated surface sites. H217O can be used to selectively enrich surface sites, allowing only these particular active sites to be monitored in a chemical process. 17O NMR spectra of thermally treated nanosized ceria clearly show how different oxygen species interconvert at elevated temperature. Density functional theory calculations confirm the assignments and reveal a strong dependence of chemical shift on the nature of the surface. These results open up new strategies for characterizing nanostructured oxides and their applications.

Synergism between the Lewis and Brönsted acid sites on HZSM-5 zeolites in the conversion of methylcyclohexane

Abstract Catalytic conversion of methylcyclohexane was studied on four specially designed HZSM-5 zeolites. A careful steam treatment was used to produce pair-sites composed of a Lewis acid site, due to extra-framework Al species from the dealumination by steaming, and a Bronsted acid site, due to bridging hydroxyl in the steamed HZSM-5. The spatial proximity of these component acid sites of the pair-site was verified by 1H double quantum magic spinning NMR. Product selectivities of methylcyclohexane conversion showed the same trend for all the samples, which indicated that the pores of the zeolites were not changed by the steam treatment. The Lewis acid site that was created, however, gave a synergistic effect with the Bronsted acid site in the pair-site, which gave higher conversions and cracking rates of methylcyclohexane. The rate of methylcyclohexane conversion increased with increased concentration of extra-framework Al, which gave more pair-sites.

A sintering-resistant Pd/SiO2 catalyst by reverse-loading nano iron oxide for aerobic oxidation of benzyl alcohol

An efficient and simple method, depositing nano iron oxide onto the surface of Pd/SiO2, to construct sintering-resistant Pd nanocatalysts was presented. The introduction of nano iron oxide not only promoted the sintering-resistance of Pd nanoparticles, but also increased the boundary between the Pd and iron oxide. The resultant catalysts exhibited enhanced catalytic activity for aerobic oxidation of benzyl alcohol.

High selectivity top-chloroaniline in the hydrogenation ofp-chloronitrobenzene on Ni modified carbon nitride catalyst

Abstract A nanocomposite composed of Ni modified carbon nitride was synthesized and used in the hydrogenation of p -chloronitrobenzene. H/D exchange demonstrated that the hydrogen chemisorbed on the surface of this nanocomposite catalyst had a hydrogen atom density of 0.65/nm 2 . It was active for hydrogenation but its activity was inferior to the hydrogen adsorbed on a Ni/Al 2 O 3 catalyst. Catalytic tests showed that this catalyst possessed a lower activity than Ni/Al 2 O 3 but the selectivity towards p -chloroaniline was above 99.9%. Even at high conversion, the catalyst maintained high selectivity, which was attributed to the unique surface property of the catalyst and the absence of a site for the adsorption of p -chloronitrobenzene, which prevents the C–Cl bond from breaking.

Probing Local Structure of Layered Double Hydroxides with 1H Solid-State NMR Spectroscopy on Deuterated Samples

By using a simple and efficient deuteration process, (2)H has been successfully introduced into layered double hydroxides (LDHs). Due to significantly less (1)H-(1)H homonuclear dipolar coupling, high-resolution (1)H solid-state NMR spectra can now be obtained conveniently at medium to low spinning speed to extract the information of cation ordering in LDHs. Furthermore, we show that double-resonance experiments can be applied easily to investigate internuclear proximities and test possible cation-ordered superstructure models. This approach can be readily extended to LDHs with different compositions to explore the local structure and the key interactions between the cations in the layer and interlayer anions.

Direct conversion of corn cob to formic and acetic acids over nano oxide catalysts

Abstract Considering energy shortage, large molecules in corn cob and easy separation of solid catalysts, nano oxides are used to transform corn cob into useful chemicals. Because of the microcrystals, nano oxides offer enough accessible sites for cellulose, hemicellulose and monosaccharide from corn cob hydrolysis and oxidant. Chemical conversion of corn cob to organic acids is investigated over nano ceria, alumina, titania and zirconia under various atmospheres. Liquid products are mainly formic and acetic acids. A small amount of other compounds, such as D-xylose, D-glucose, arabinose and xylitol are also detected simultaneously. The yield of organic acids reaches 25%–29% over the nano oxide of ceria, zirconia and alumina with 3 h reaction time under 453 K and 1.2 MPa O2. The unique and fast conversion of corn cob is directly approached over the nano oxides. The results are comparative to those of biofermentation and offer an alternative method in chemically catalytic conversion of corn cob to useful chemicals in a one-pot chemical process.

Catalytic Ammonia Synthesis over Mo Nitride/ZSM‐5

Molybdenum nitride species in HZSM‐5 are prepared by the reaction of ammonia with MoOx, which is pre‐exchanged into the channel of HZSM‐5. Both the processes of solid exchange of molybdenum oxide with the zeolite and the ammonia reaction are monitored by mass spectrometry. The Mo/N ratio of the MoNx species in the Mo nitride/HZSM‐5 is close to 2, as measured by temperature‐programmed oxidation. The MoNx species are more stable than bulk Mo2N against oxidation, due to the interaction between the molybdenum nitride species and the charged zeolite framework. The MoNx species, of which the dispersion is found to be greater than 90 %, are very active in ammonia synthesis and the catalytic activity is much more stable than that of bulk Mo2N. The reaction pressure is much more favorable to ammonia formation on the MoNx/ZSM‐5 catalyst than on bulk Mo2N. The interaction of nitrogen molecules with the inner electric field of the zeolite, at an equivalent pressure, enhances the reaction of ammonia synthesis.

3D charged grid induces a high performance catalyst: ruthenium clusters enclosed in X-zeolite for hydrogenation of phenol to cyclohexanone

The hydrogenation of phenol to cyclohexanone is an important industrial reaction and supported palladium catalysts are the most popular catalysts applied nowadays. Hitherto, there has been no success in using ruthenium catalysts for this reaction because of their poor catalytic performance, in spite of the fact that ruthenium is a frequently used metallic component in hydrogenation catalysts. Herein, we report our effort in creating a meso-structured catalyst composed of ruthenium clusters enclosed in the super cages of X-zeolite, which is prepared by mixing precursors of ruthenium and X-zeolite at the beginning stage of preparation, i.e., before the crystallization of the zeolite. This well-defined Ru catalyst exhibits excellent catalytic performance for the selective hydrogenation of phenol, similar to palladium catalysts. The results demonstrate that the joint effects of the 3D negatively charged grid of X-zeolite and the enclosed electron-deficient ruthenium clusters enhance the activity of metallic ruthenium and suppress the further hydrogenation of the valuable product cyclohexanone, which is not possible with traditional Ru catalysts. This investigation reveals the fact that although catalytic reactions are always initiated on the active centers of the catalyst at dimensions on the atomic scale, the effect of the neighboring environment surrounding the active species might extend it to the meso-scale, which should not be ignored as it might induce electronic and structural changes in the active species as well as possibly dramatic changes in the performance of the catalyst. The meso-structured catalyst integrated active species and the neighboring environment as a whole should be considered in discussing the performance of catalysts.