Qingxiang Ma

Sol-gel Auto-combustion Synthesis of Ni-CexZr1-xO2 Catalysts for Carbon Dioxide Reforming of Methane

Carbon dioxide reforming of methane (methane dry reforming) over Ni–Ce0.8Zr0.2O2 catalysts prepared by a sol–gel auto-combustion method and a conventional co-precipitation method were comparatively studied. We show that sol–gel auto-combustion is very promising for preparing thermal stable homogeneous mixed metal oxide catalysts. The auto-combustion synthesized catalyst exhibited higher initial activity and stability due to its smaller Ni crystalline size and intimate interaction between Ni and Ce0.8Zr0.2O2. In contrast, the co-precipitated catalyst showed poor activity and deactivated rapidly. The rapid deactivation was caused by a higher graphitization degree of the deposited carbon over co-precipitated catalyst with larger Ni crystalline size. We also found that the physico-chemical properties and catalytic activity of sol–gel auto-combustion synthesized catalysts were closely related to the metal nitrate (MN)/citric acid (CA) ratio. High MN/CA ratio led to more violent combustion behaviour and an accordingly higher degree of crystallization of the synthesized catalyst. In contrast, a low MN/CA ratio resulted in more carbon species residues and poor catalytic performance. The Ce/Zr ratio also had a profound influence on the phase structure, reducibility, oxygen vacancies and catalytic performance of Ni–Ce0.8Zr0.2O2 catalysts. Ni–Ce0.8Zr0.2O2 catalyst with cubic phase exhibited the best catalytic performance because of high reducibility, high Ni dispersion and strong Ni-CexZr1−xO2 interaction, and considerable amounts of oxygen vacancies.

Effects of zinc on Fe-based catalysts during the synthesis of light olefins from the Fischer-Tropsch process

Abstract Fe-based catalysts for the production of light olefins via the Fischer-Tropsch synthesis were modified by adding a Zn promoter using both microwave-hydrothermal and impregnation methods. The physicochemical properties of the resulting catalysts were determined by scanning electron microscopy, the Brunauer-Emmett-Teller method, X-ray diffraction, H 2 temperature-programed reduction and X-ray photoelectron spectroscopy. The results demonstrate that the addition of a Zn promoter improves both the light olefin selectivity over the catalyst and the catalyst stability. The catalysts prepared via the impregnation method, which contain greater quantities of surface ZnO, exhibit severe carbon deposition following activity trials. In contrast, those materials synthesized using the microwave-hydrothermal approach show improved dispersion of Zn and Fe phases and decreased carbon deposition, and so exhibit better CO conversion and stability.

Fabrication of active Cu–Zn nanoalloys on H-ZSM5 zeolite for enhanced dimethyl ether synthesis via syngas

One-step conversion of CO and H2 to dimethyl ether (DME) is still challenging to date. This work describes a promising bifunctional Cu/ZnO/H-ZSM5 catalyst prepared by a novel bimetallic sputtering method for such conversions. The sputtered catalyst consisted of well-dispersed Cu–ZnO nanoparticles of about 5 nm, which were physically anchored on an acidic zeolite support. The weak interaction between the deposited metal and zeolite clearly lowered the reduction temperature by 50 °C. After H2 reduction, a unique Cu–Zn nanoalloy layer was observed on the surface of the Cu–ZnO nanoparticles, reducing the activation energy of CO adsorption. The surface alloy layer and inner Cu–ZnO sites play a cooperative catalytic role in improving the CO conversion and promoting DME selectivity. Compared to conventional impregnated catalysts, the CO conversion was enhanced by almost four times and the DME selectivity was promoted to as high as 92.1%. The proposed concept is beneficial for developing highly-active catalysts with bimetallic components supported on a functional support.

Ordered mesoporous alumina-supported bimetallic Pd–Ni catalysts for methane dry reforming reaction

To compare the influence of Pd addition to Ni supported on ordered mesoporous alumina catalyst, prepared highly ordered mesoporous alumina (MA) was used as catalyst support for methane dry reforming under atmospheric pressure. Ni and Pd were impregnated on this support to obtain both monometallic and/or bimetallic catalysts, respectively. The fresh and spent catalysts were characterized by N2 physical adsorption, high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), laser Raman spectroscopy and temperature-programmed hydrogenation (TPH). The XRD and HRTEM analysis results showed that Ni–Pd nanoalloy was formed after H2 reduction. The catalytic performance analysis results indicated that the bimetallic nanoalloy catalysts showed higher activity than the monometallic catalyst. The deposition of carbon during the reaction was analyzed. The results indicated that different supported metal species led to different carbon species which influenced catalytic performance.

Effect of preparation of Fe–Zr–K catalyst on the product distribution of CO2 hydrogenation

The precursors of Fe–Zr–K catalysts were prepared by microwave assisted homogeneous precipitation followed by incipient wetness impregnation. The obtained mesoporous particles were small and uniformly shaped. After reduction, the catalyst showed high activity for the selective production of light olefins from CO2 hydrogenation, superior to the catalyst obtained by co-precipitation. Characterization indicated that with Zr addition, the reducibility, surface basicity and surface atomic composition of the samples varied with the Zr content. The CO2 adsorption ability of the samples was increased and the samples became hard to reduce as a result of the interaction between iron species and zirconia. In the case of using 5Fe–1Zr–K under selected conditions of 1000 h−1, 320 °C and 2 MPa, the CO2 conversion and the selectivity of C2–C4 olefins reached 54.36% and 53.63%. The olefin/paraffin ratio in the C2–C4 hydrocarbon product fraction reached 6.44. The selectivity of CO and C5+ hydrocarbons were 3% and 19.78%, respectively. The catalytic activity remained stable up to 92 h in time-on-stream reaction.

Hydrothermal preparation of Fe–Zr catalysts for the direct conversion of syngas to light olefins

Fe/Zr precursors were prepared by a one-step and two-step hydrothermal process respectively, following K promotion by incipient wetness impregnation, which then were used for the selective production of C2–C4 olefins via Fischer–Tropsch synthesis from syngas. The textural properties, phase structure, reduction behavior and the catalytic performance of the obtained catalyst samples were greatly affected by different preparation procedures. The T–Fe/Zr samples prepared by the two-step hydrothermal process caused a decrease in the surface area and easier reduction of iron species compared with that of the O–Fe/Zr samples prepared by the one-step hydrothermal process. The T–Fe/Zr samples before and after K promotion showed preferred orientation along the (−111) and (111) lattice planes of ZrO2 in contrast to the ZrO2 (101) lattice plane on O–Fe/Zr samples. For CO hydrogenation, all the catalysts exhibited high activity and good stability. The T–Fe/Zr–K catalysts with highly dispersed zirconia on the iron surface could prevent Fe–Zr mixed oxide formation by decreasing the interaction between iron and zirconia, leading to a slight increase in C2–C4 olefin selectivity and improvement on the product distribution.

Functionalized Natural Carbon-Supported Nanoparticles as Excellent Catalysts for Hydrocarbon Production

We report a one-pot and eco-friendly synthesis of carbon-supported cobalt nanoparticles, achieved by carbonization of waste biomass (rice bran) with a cobalt source. The functionalized biomass provides carbon microspheres as excellent catalyst support, forming a unique interface between hydrophobic and hydrophilic groups. The latter, involving hydroxyl and amino groups, can catch much more active cobalt nanoparticles on surface for Fischer-Tropsch synthesis than chemical carbon. The loading amount of cobalt on the final catalyst is much higher than that prepared with a chemical carbon source, such as glucose. The proposed concept of using a functionalized natural carbon source shows great potential compared with conventional carbon sources, and will be meaningful for other fields concerning carbon support, such as heterogeneous catalysis or electrochemical fields.

A Zinc Cobalt Sulfide Nanosheet Array Derived from a 2D Bimetallic Metal-Organic Frameworks for High-Performance Supercapacitors

Porous ternary metal sulfide integrated electrode materials with abundant electroactive sites and redox reactions are very promising for supercapacitors. Herein, a porous zinc cobalt sulfide nanosheet array on Ni foam (Zn-Co-S/NF) was constructed by facile growth of 2D bimetallic zinc/cobalt-based metal-organic framework (Zn/Co-MOF) nanosheets with leaf-like morphology on NF, followed by additional sulfurization. The Zn-Co-S/NF nanosheet array acted directly as a supercapacitor electrode showing much better electrochemical performance (2354.3 F g-1 and 88.6 % retention over 1000 cycles) when compared with zinc cobalt sulfide powder (355.3 F g-1 and 75.8 % retention over 1000 cycles), which originates from good electrical conductivity and mechanical stability, abundant electroactive sites, and facilitated transportation of electrons and electrolyte ions due to the unique nanosheet array structure. An asymmetric supercapacitor (ASC) device assembled from Zn-Co-S/NF and activated carbon electrodes can deliver a highest energy density of 31.9 Wh kg-1 and a maximum power density of 8.5 kW kg-1 . Most importantly, this ASC also shows good cycling stability (71.0 % retention over 10000 cycles). Furthermore, a red LED can be powered by two connected ASCs, and thus as-synthesized Zn-Co-S/NF has great potential for practical applications.

Preparation of layered K/Mg-Fe-Al catalysts and its catalytic performances in CO hydrogenation

Abstract A series of K promoted K/MgFeAl-HTLcs catalysts with different Mg/Fe/Al molar ratios were prepared by means of coprecipitation and impregnation method for direct synthesis of light olefins from CO hydrogenation. The samples were characterized by XRD, N2 adsorption-desorption, SEM, TG, H2-TPR and XPS measurements. The results show that MgFeAl-HTLcs catalyst precursors have typical layered structure. MgO, Fe2O3 and small amount of MgFeAlO4 are formed after calcination. MgCO3 and Fe3O4 could be observed after reaction, and a little Fe5C2 iron carbide with broad and weak peaks appears simultaneously. Thermal stability of K/MgFeAl-HTLcs is improved due to recovery of hydrotalcite-like structure after K promotion. With increase of Al content, specific surface area of the precursors decreases monotonically after structure reconstruction. Reduction of Fe2O3 to Fe3O4 is inhibited with addition of Al, compared with K/Mg-Fe sample. Fe enrichment before reaction and K enrichment after reaction are observed on secondary calcination samples. During CO hydrogenation, the prepared samples show high activity and C2=-C4= selectivity with low C5+ weight fraction. C5+ hydrocarbons decrease and olefin selectivity increases with increasing Fe/Al molar ratio. The C5+ decreases from 22.17% to 10.90%, and C2=-C4= weight content increases from 40.98% to 47.28% on K/1.5Mg-0.67Fe-0.33Al sample compared with that of K/1.5Mg-0.67Fe sample.