Tungsten Promoted Ni/Al_2O_3 Catalysts for Carbon Dioxide Reforming of Methane to Synthesis Gas

A series of tungsten promoted alumina supported nickel catalysts has been prepared for the carbon dioxide reforming of methane to synthesis gas. The catalysts have been characterized by means of XRD, TEM, and Laser Raman spectroscopy. It is shown that the addition of tungsten to the nickel catalyst can stabilize the catalyst and increase the resistance to carbon deposition. Adding a suitable amount of tungsten can also increase the catalyst activity to be close to that of supported noble metal catalysts. The carburisation of the tungsten modified nickel catalyst decreases the catalyst activity at lower reaction temperatures(<1123K), but has no effect on the catalyst performance at higher reaction temperatures. The alumina supported nickel catalyst modified by 0.67%(mass fraction) WO_3 has the equivalent equilibrium constant of the dry reforming reaction to that of alumina supported 5%(mass fraction) Ru at 873 K, and also has a lower activation energy for dry reforming than the latter.

Preparation of MCM-41 in Industrial Scale and Its Application in Heavy Oil Processing

A series of MCM 41 molecular sieves have been prepared on an industrial scale, and the effect of preparation factors such as aging temperature, pH values on the structure and pore distribution of the MCM 41 product have been studied by using X ray diffraction(XRD), thermogravimetric(TG) and electron microscopy(TEM). It is shown that the pH values have a significant effect on the crystallinity of the synthesized product. Under proper conditions, the MCM 41 prepared on an industrial scale has the same performance as the samples prepared on an Lab scale. The prepared MCM 41 was used as a modifier of zeolite Y for fluid catalytic cracking(FCC) of residual oil. It is shown that the addition of the MCM 41 in the zeolite Y catalyst increases the pore size, and surface area of the catalysts, which helps to increase the yield of gasoline and diesel and decrease the production of gaseous product and carbon deposition in the catalyst. The better performance of the MCM 41 modified zeolite Y catalyst is believed to be due to its adjustment on the acidity and increase of the pore size.

Probe-assisted NMR:Recent progress on the surface study of crystalline metal oxides with various terminated facets

The development of metal oxides with specific facet exposure for better catalytic performance in targeted applications has been well-documented.However,the understanding of surface structure-activity correlation is severely hindered by the current poor resolution of conventional surface characterization tools.In this mini-review,some of the latest research developments on the characterization of the surface structure and properties of faceted ZnO and TiO_(2)by probe-assisted nuclear magnetic resonance spectroscopy(NMR)are discussed.

Dehydration of sugars to 5-hydroxymethylfurfural and non-stoichiometric formic and levulinic acids over mesoporous Ta and Ta-W oxide solid acid catalysts

A series of mesoporous Ta and Ta-W oxides have been prepared and employed as solid acid catalysts for the dehydration of fructose and glucose to 5-hydroxymethylfurfural(HMF).Solid state 31 P MAS NMR spectroscopic results using trimethylphosphine(TMP)as a probe molecule show that the acid strength and the ratio of Br?nsted to Lewis acid sites increase gradually with the addition of tungsten in tantalum oxide.It is found that high sugar conversion and HMF selectivity are achieved over catalyst with relatively high ratios of Br?nsted to Lewis acid sites.Unexpected stoichiometric excess of formic acid relative to levulinic acid can be observed mainly because of direct decomposition of fructose over Lewis acid sites.The addition of 2-butanol leads to the increase of sugars conversion and the HMF selectivity,especially for the catalyst with high ratio of Br?nsted to Lewis acid sites.Among them,Ta7W3 oxide catalyst shows 54%HMF selectivity and good reusability with the addition of 2-butanol by extracting HMF from aqueous phase and removing humins deposed on the surface of the catalyst.

Effect of Bronsted/Lewis Acid Ratio on Conversion of Sugars to 5-Hydroxymethylfurfural over Mesoporous Nb and Nb-W Oxides

A series of mesoporous Nb and Nb-W oxides were employed as highly active solid acid catalysts for the con- version of glucose to 5-hydroxymethylfurfural （HMF）. The results of solid state 31p MAS NMR spectroscopy with adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number of Bronsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb-W oxides varied with the ratio of Bronsted to Lewis acid sites and high glucose conversion was observed over NbsW5 and NbTWs oxides with high ratios of Bronsted to Lewis acid sites. All Nb-W oxides show a relatively high selectivity of HMF, whereas no HMF forms over sulfuric acid due to its pure Bronsted acidity. The results indicate fast isom- erization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Bronsted acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2-butanol/H2O system enhances the HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over NbTW3 oxide. The 2-butanol/H2O catalytic system can also be employed in conversion of sucrose, achieving HMF selectivity of 46% over Nb5W5 oxide.

Chemical looping based ammonia production--A promising pathway for production of the noncarbon fuel

Ammonia, primarily made with Haber-Bosch process developed in 1909 and winning two Nobel prizes, is a promising noncarbon fuel for preventing global warming of 1.5 °C above pre-industrial levels. However,the undesired characteristics of the process, including high carbon footprint, necessitate alternative ammonia synthesis methods, and among them is chemical looping ammonia production(CLAP) that uses nitrogen carrier materials and operates at atmospheric pressure with high product selectivity and energy efficiency. To date, neither a systematic review nor a perspective in nitrogen carriers and CLAP has been reported in the critical area. Thus, this work not only assesses the previous results of CLAP but also provides perspectives towards the future of CLAP. It classifies, characterizes, and holistically analyzes the fundamentally different CLAP pathways and discusses the ways of further improving the CLAP performance with the assistance of plasma technology and artificial intelligence(AI).

Improving Catalytic Stability and Coke Resistance of Ni/Al_(2)O_(3) Catalysts with Ce Promoter for Relatively Low Temperature Dry Reforming of Methane Reaction

A series of Ni catalysts supported on alumina with different Ce contents(1.0%–6.0%,mass fraction)was prepared by the impregnation method and used for dry reforming of methane(DRM)at a relatively low temperature of 650°C.The promotion effect of Ce with different loading amounts on the physicochemical properties of the catalysts was systematically characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD),N_(2) adsorption-desorption,thermo elemental IRIS Intrepid inductively coupled plasma atomic emission spectrometer(ICP-AES),UV-visible diffuse reflectance spectroscopy(UV-Vis DRS),Fourier transformation infrared(FTIR)spectra,H_(2)-temperature programmed reduction(H_(2)-TPR)analysis,H_(2)-temperature programmed desorption(H_(2)-TPD),and The X-ray photoelectron spectroscopy(XPS)techniques.The results indicate that all the catalysts mainly exist in the NiAl_(2)O_(4) phase after being calcined at 750°C with small Ni particle sizes due to the strong metal-support interaction derived from the reduction of the NiAl_(2)O_(4) phase.The Ce-promoted catalysts show better catalytic performance as well as the resistance against sintering of Ni particles and deposition of carbon compared to the Ni/Al_(2)O_(3) catalyst.The Ni-6Ce/Al_(2)O_(3) exhibits the best catalytic stability and coke resistance among the four catalysts studied,which is due to its small Ni nanoparticles sizes,excellent reducibility as well as high amount of active oxygen species.In a 400 h stability test for DRM reaction at 650°C,Ni-6Ce/Al_(2)O_(3) exhibits less coke deposition and small growth of Ni nanoparticles.This work provides a simple way to preparing the Ni-Ce/Al_(2)O_(3) catalyst with enhanced catalytic performance in DRM.The Ni-6Ce/Al_(2)O_(3) catalyst has great potential for industrial application due to its anti-sintering ability and resistance to carbon deposition.