Weiping Fang

Effects of composite oxide supports on catalytic performance of Ni-based catalysts for CO methanation

Metal-oxide-modified NiO/Al2O3 catalysts for methanation of CO were prepared using a modified grinding-mixing method and characterized using X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption isotherms, temperature-programmed reduction by H2, temperature-programmed desorption by H2, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results show that the activity of an MgO-modified NiO/Al2O3 catalyst is better than those of NiO/ZrO2-Al2O3 and NiO/SiO2-Al2O3 in the reaction temperature range 300–700 °C. The incorporation of a metal oxide into NiO/Al2O3 was found to weaken Ni–Al interactions, leading to generation of large numbers of active Ni species, and this was confirmed to be responsible for the improvement in the performances of the catalysts in the methanation reaction.

Effect of Mg/Al atom ratio of support on catalytic performance of Co-Mo/MgO-Al2O3 catalyst for water gas shift reaction

Abstract Co-Mo-based catalysts supported on mixed oxide supports MgO-Al 2 O 3 with different Mg/Al atom ratios for water gas shift reaction were studied by means of TPR, Raman, XPS and ESR. It was found that the octahedral Mo species in oxidized Co-Mo/MgO(x)-Al 2 O 3 catalyst and the contents of Mo 5+ , Mo 4+ , S 2− and S 2− 2 species in the functioning catalysts increased with increasing the Mg/Al atom ratio of the support under the studied experimental conditions. This is favorable for the formation of the active Co-Mo-S phase of the catalysts. Catalytic performance testing results showed that the catalysts Co-Mo/MgO-Al 2 O 3 with the Mg/Al atom ratio of the support in the range of 0.475–0.525 exhibited optimal catalytic activity for the reaction.

Quantitative nucleation and growth kinetics of gold nanoparticles via model-assisted dynamic spectroscopic approach

Lacking of quantitative experimental data and/or kinetic models that could mathematically depict the redox chemistry and the crystallization issue, bottom-to-up formation kinetics of gold nanoparticles (GNPs) remains a challenge. We measured the dynamic regime of GNPs synthesized by l-ascorbic acid (representing a chemical approach) and/or foliar aqueous extract (a biogenic approach) via in situ spectroscopic characterization and established a redox-crystallization model which allows quantitative and separate parameterization of the nucleation and growth processes. The main results were simplified as the following aspects: (I) an efficient approach, i.e., the dynamic in situ spectroscopic characterization assisted with the redox-crystallization model, was established for quantitative analysis of the overall formation kinetics of GNPs in solution; (II) formation of GNPs by the chemical and the biogenic approaches experienced a slow nucleation stage followed by a growth stage which behaved as a mixed-order reaction, and different from the chemical approach, the biogenic method involved heterogeneous nucleation; (III) also, biosynthesis of flaky GNPs was a kinetic-controlled process favored by relatively slow redox chemistry; and (IV) though GNPs formation consists of two aspects, namely the redox chemistry and the crystallization issue, the latter was the rate-determining event that controls the dynamic regime of the whole physicochemical process.

Water gas shift activity of Co-Mo/MgO-Al2O3 catalysts presulfided with ammonium sulfide

Abstract Co-Mo/MgO-Al2O3 catalyst was presulfided with ammonium sulfide in aqueous solution and activated with synthesis gas for water gas shift reaction. The assay results indicate that the presulfided Co-Mo/MgO-Al2O3 catalyst exhibits an excellent catalytic activity and stability. XRD and EPR characterization results show that the O-S exchange might occur during the impregnation, leading to the formation of (NH4)2MoS4(or (NH4)2MoxSy) precursor, which was then thermally decomposed and reduced to MoS2. The higher catalytic performance is attributed to an optimization formation of active Co-Mo sulfides, consisting of well dispersed MoS2 and Co-Mo-S phase due to the redispersion of Co sulfide particles over the edges of newly formed MoS2 crystallites.

Low temperature CO oxidation on Ni-promoted CuO-CeO2 catalysts

Abstract A series of Ce 20 Cu 5 Ni y O x catalysts for CO oxidation at low temperature were prepared and characterized by N 2 adsorption, X-ray diffraction, temperature-program reduction by H 2 , X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Ce 20 Cu 5 Ni 0.4 O x exhibited the highest catalytic activity. The addition of NiO increased the amount of copper ions doped into the CeO 2 matrix and gave more oxygen vacancies in ceria by the formation of a Ni-O-Ce solid solution. XPS results showed that large quantities of Cu + , Ce 3+ , and lattice oxygen existed in the fresh Ce 20 Cu 5 Ni 0.4 O x catalyst. Cu + ions in the catalyst can easily migrate to the ceria lattice to form a Cu-O-Ce solid solution, which enhanced the release of the lattice oxygen of the oxides under a reducing atmosphere. The high catalytic activity of Ce 20 Cu 5 Ni 0.4 O x is due to the promoter giving increased amounts of Cu + in the catalyst and the formation of solid solutions of both Cu-O-Ce and Ni-O-Ce.

Promoting effect of dual modification of H-ZSM-5 catalyst by alkali treating and Mg doping on catalytic performances for alkylation of benzene with ethanol to ethylbenzene

Alkali-treated HZSM-5 zeolite (AT) was modified with Mg species to produce combined modified HZSM-5 catalyst (Mg-AT) for alkylation of benzene with ethanol to ethylbenzene. The catalysts were tested and characterized by X-ray diffraction (XRD), NH3-Temperature Programmed Desorption (NH3-TPD), Nitrogen adsorption–desorption, Magic angle spinning nuclear magnetic resonance (MAS NMR) and Scanning Electron Microscope (SEM) techniques. The characterization results showed that for the combined modified HZSM-5 sample, the ratio of surface area of mesopores to the total surface area was the highest. The Mg (1 wt%)-AT catalyst was found to exhibit the highest activity (30% of the conversion of benzene) and selectivity to EB (92%) for the reaction, which was confirmed to be due to the proper L/B acid proportion (3.79) and the improvement of the mesopores of the catalyst.

Methanation of carbon dioxide over the LaNiO3 perovskite catalysts activated under the reactant stream

Abstract In this study, LaNiO 3 perovskite catalysts were prepared by citrate method and used for carbon dioxide (CO 2 ) methanation. The catalysts were activated at different temperatures (400–700°C) under the reactant stream. The activation led to the formation of small metallic nickel particles and hexagonal lanthanum oxocarbonate (La 2 O 2 CO 3) . Ni 0 was highly dispersed and enveloped by La 2 O 2 CO 3 , which was responsible for the high catalytic activity and stability of the LaNiO 3 perovskite catalysts even at high temperature (400–500°C). The X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and H 2 -temperature-programmed desorption measurements illustrated that La 2 O 2 CO 3 generated from the activation might play an important role in the methanation of CO 2 .

Potassium-decorated active carbon supported Co-Mo-based catalyst for water-gas shift reaction

Abstract The effect of potassium-decoration was studied on the activity of water-gas shift (WGS) reaction over the Co-Mo-based catalysts supported on active carbon (AC), which was prepared by incipient wetness co-impregnation method. The decoration of potassium on active carbon in advance enhances the activities of the CoMo-K/AC catalysts for WGS reaction. Highest activity (about 92% conversion) was obtained at 250 °C for the catalyst with an optimum K2O/AC weight ratio in the range from 0.12 to 0.15. The catalysts were characterized by TPR and EPR, and the results show that activated carbon decorated with potassium makes Co-Mo species highly dispersed, and thus easily reduced and sulfurized. XRD results show that an appropriate content of potassium-decoration on active carbon supports may favors the formation of highly dispersed Co9S8-type structures which are situated on the edge or a site in contact with MoS2, K-Mo-O-S, Mo-S-K phase. Those active species are responsible for the high activity of CoMo-K/AC catalysts.

Promoting effect of a Cu–Zn binary precursor on a ternary Cu–Zn–Al catalyst for methanol synthesis from synthesis gas

Small amounts of Cu–Zn binary precursor were introduced into traditional ternary Cu–Zn–Al catalysts to produce a series of modified ternary Cu–Zn–Al catalysts for the synthesis of methanol from synthesis gas with high CO content. 2 wt% Cu–Zn (Cu–Zn = 3 : 1 atomic ratio) binary precursor was found to have the most significant improvement for the catalytic performances. Physicochemical characterization of the as-prepared catalysts by TPR, in situ XRD and in situ XAES techniques indicated that the addition of a suitable amount of binary Cu–Zn precursor partially modified the structure of the catalyst, changed the particle size of Cu, copper surface area and the ratio of Cu+/Cu0, and thus effectively improved the catalytic performances of the catalyst.

Effect of preparation methods of aluminum emulsions on catalytic performance of copper-based catalysts for methanol synthesis from syngas

Abstract Various Cu/ZnO/Al2O3 catalysts have been synthesized by different aluminum emulsions as aluminum sources and their performances for methanol synthesis from syngas have been investigated. The influences of preparation methods of aluminum emulsions on physicochemical and catalytic properties of catalysts were studied by XRD, SEM, XPS, N2 adsorption-desorption techniques and methanol synthesis from syngas. The preparation methods of aluminum emulsions were found to influence the catalytic activity, CuO crystallite size, surface area and Cu0 surface area and reduction process. The results show that the catalyst CN using the aluminum source prepared by addition the ammonia into the aluminum nitrate (NP) exhibited the best catalytic performance for methanol synthesis from syngas.