Jinghong Zhou

Kinetics of heterogeneous oxidation of concentrated ammonium sulfite

Abstract The heterogeneous oxidation of ammonium sulfite solution was investigated in stirred cell and packing column. The concentration range of sulfite is 0.05–4.7gmol/l and that of oxygen in the gas phase is 21–100%, temperature range is 30–75°C. The results indicated that there is a critical sulfite concentration, below which the reaction order with respect to sulfite is 0.2, while above which the order turns to −1.0. The reaction order with respect to oxygen is 1. Apparently, the ionic strength was found to inhibit the oxidation. The apparent energy of activation determined is 32.7kJ/mol.

Ir–Re alloy as a highly active catalyst for the hydrogenolysis of glycerol to 1,3-propanediol

In this work, bimetallic Ir–Re catalysts supported on KIT-6 are prepared by tuning the thermal treatment procedures, i.e., conventional calcination and reduction (Ir–Re/KIT-6-CR) and modified direct reduction (Ir–Re/KIT-6-R) after impregnation of two metal precursors. The structure of both catalysts is intensively characterized by H2-TPR, STEM-HAADF-EDX, XPS and CO-DRIFTS. Results indicate that an Ir–Re alloy forms on the KIT-6 support when direct reduction is employed, which exhibits excellent catalytic performance in hydrogenolysis of glycerol. The formation rate of 1,3-propanediol over Ir–Re/KIT-6-R reaches 25.6 mol1,3-PD molIr−1 h−1 at 63% glycerol conversion with the addition of amberlyst-15 under 8 MPa H2, 393 K and 20 wt% glycerol aqueous solution, almost twice that over Ir–Re/KIT-6-CR. It is revealed that Re species without prior calcination treatment could be fully reduced and therefore couple with Ir to form an Ir–Re alloy structure with enhanced resistance against particle aggregation, while the calcination and subsequent reduction leads to the formation of an Ir–ReOx structure since the rhenium oxide species generated during the calcination is difficult to be reduced.

Carbon Nanofiber-Supported Ru Catalysts for Hydrogen Evolution by Ammonia Decomposition

Abstract Carbon nanofibers (CNFs) with fish-bone graphene alignment and carbon nanotubes (CNTs) were used to support ruthenium for ammonia decomposition. The Ru nanoparticles on the CNF supports are more active than those on CNT supports. The Ru particle size was adjusted by changing the Ru loading or by introducing oxygen containing groups onto the CNF surface. The site activity increases when the Ru crystal size increases. The oxygen groups on the CNFs have a remarkable effect on ammonia decomposition over the Ru nanoparticles. On identically sized Ru crystals, oxygen on the CNFs clearly enhances ammonia decomposition over the Ru/CNFs.

Hydrogenolysis of sorbitol to glycols over carbon nanofibers-supported ruthenium catalyst: The role of base promoter

Abstract Sorbitol hydrogenolysis over carbon nanofibers-supported Ru (Ru/CNFs) was carried out with different bases (NaOH, KOH, Mg(OH)2, Ba(OH)2, and CaO) to investigate the role of base promoter. The results indicated that all the bases used significantly enhanced the sorbitol conversion while the glycol selectivities varied with the base type and amount. CaO was the best base in terms of glycol selectivity for two reasons. CaO provided OH− for the base-promoted cleavage of C–C bonds, while it also supplied Ca2+ for complexation with the intermediate aldehydes, thus affecting the reaction pathways. We identified an optimum ratio among sorbitol concentration, Ru/CNFs catalyst, and CaO to achieve favorable glycol selectivities in sorbitol hydrogenolysis. Reaction pathways for sorbitol hydrogenolysis into glycols in aqueous solution in the presence of CaO have been proposed based on the mechanistic study.

Effects of pretreatment temperature on bimetallic Ir-Re catalysts for glycerol hydrogenolysis

Abstract A series of bimetallic Ir-Re/KIT-6 catalysts was prepared by direct activation of impregnated samples at various reduction temperatures to study the effect of pretreatment temperature on catalyst structure and on catalytic performance for glycerol hydrogenolysis. All catalysts were characterized by N2 adsorption-desorption, transmission electron microscopy, CO chemisorption, in-situ CO adsorption diffuse reflectance infrared Fourier transform spectroscopy and temperature-programmed desorption of ammonia (NH3-TPD). The results demonstrated that those catalysts reduced at 400 to 700 °C exhibited an Ir-Re alloy structure with similar particle sizes and Ir dispersions. Furthermore, NH3-TPD results indicated that all catalysts had similar acid strengths, though acid density varied with the reduction temperature. Increasing the pretreatment temperature from 400 to 600 °C monotonically increased the acid density of the catalysts and also improved the catalytic activity for glycerol hydrogenolysis. Reducing the Ir-Re alloy catalyst at 700 °C slightly decreased the activity due to the growth of the metal particles. Moreover, a linear relationship was identified between the acid density of a catalyst and its activity, verifying the vital roles of both Re and surface acidity with regard to optimizing the performance of Ir-Re alloy catalysts.

Palladium Catalysts Supported on Fishbone Carbon Nanofibers from Different Carbon Sources

Abstract Pd catalysts (0.5% Pd) supported on fishbone carbon nanofibers (FCNFs) from different carbon sources for terephthalic acid (TA) hydro-purification were prepared and investigated. CNFs from various carbon sources, CO (FCNF-CO), CH 4 (FCNF-C1), and C 2 H 4 (FCNF-C2), have been synthesized and characterized by N 2 adsorption, XRD, and TPD-MS. The results indicated that though they all possess similar fishbone structure, the FCNF from CO has the largest specific surface area, highest graphitization degree, and a large amount of surface groups, while the FCNF from C 2 H 4 has the least specific surface area, lowest graphitization degree, and moderate surface groups. Pd/CNFs were synthesized and characterized by TEM, N 2 adsorption, XRD, and CO chemisorption. The catalytic activity for TA purification follows the sequence Pd/FCNF-CO > Pd/FCNF-C1 > Pd/FCNF-C2, which is in accordance with the sequence of Pd dispersion. It is believed that rather than the graphene arrangement, the synergic support effect of pore structure, crystallinity, and the surface chemistry dictates the Pd dispersion on FCNF and the consequent catalytic activity.

Sorbitol Hydrogenolysis to Glycols over Carbon Nanofibers/Graphite-felt Composite-supported Ru Catalyst in a Trickle Bed Reactor

Abstract Carbon nanofibers were in-situ grown on graphite-felt, and then Ru was supported to synthesize Ru/CNFs/GF structured catalyst. The comparisons of pressure gradient and reaction results clearly indicated that the Ru/CNFs/GF structured catalyst was more proper than powdered Ru/CNFs catalyst for sorbitol hydrogenolysis in a trickle bed reactor. For the structured catalyst, increasing the linear velocities would increase the sorbitol conversion, but only slightly change the glycols selectivity, which was due to the intensified mass transfer. Nevertheless, increasing the thickness of the carbon nanofibers layer would significantly decrease the glycols selectivity, which was due to the increased diffusion distance for hydrogen and glycols in the mesopores of the carbon nanofibers layer.

Boosting Size‐Selective Hydrogen Combustion in the Presence of Propene Using Controllable Metal Clusters Encapsulated in Zeolite

A strategy is presented for making metal clusters encapsulated inside microporous solids selectively accessible to reactant molecules by manipulating molecular sieve size and affinity for adsorbed molecules. This expands the catalytic capabilities of these materials to reactions demanding high selectivity and stability. Selective hydrogen combustion was achieved over Pt clusters encapsulated in LTA zeolite (KA, NaA, CaA) in a propene-rich mixture obtained from propane dehydrogenation, showing pore-size dependent selectivity and coking rate. Propene tended to adsorb at channels or external surfaces of zeolite, interfering the diffusion of hydrogen and oxygen. Tailoring the surface of LTA zeolite with additional alkali or alkaline earth oxides contributed to narrowing zeolite pore size and their affinity for propene. The thus-modified Pt@KA catalyst displayed excellent hydrogen combustion selectivity (98.5 %) with high activity and superior anti-coking and anti-sintering properties.