Selectivity For Methanol Decomposition Research Articles

Nanostructured copper-zirconia composites as catalysts for methanol decomposition

Nanostructured mesoporous ZrO2 was obtained by hydrothermal synthesis using surfactant assisted approach. Copper modifications of thus obtained ZrO2 (4–25wt.% copper) were prepared by incipient wetness impregnation with the corresponding nitrate or acetyl acetonate precursors and further treatment in oxidative or reduction atmosphere. The obtained materials were characterized by N2 physisorption, XRD, UV–vis, FTIR, XPS and temperature programmed reduction with hydrogen and tested as catalysts in methanol decomposition to hydrogen and CO. Selected samples were investigated after partial coverage of the surface with 11C-labeled methanol and 11C-labeled methyl formate. The formation of monolayer of finely dispersed copper oxide species on zirconia at about 4wt.% copper loading and bulk copper nanoparticles at higher one is observed. It was assumed that zirconia support provides the formation of two types of catalytic sites: the first ones strongly adsorb methanol and exhibit predominantly dehydrogenation activity, while the others, possess acidic function. The modification of zirconia with copper significantly improves the catalytic activity and selectivity in methanol decomposition via (i) creation of additional surface acidic sites which contribute to generation of methoxy intermediates; (ii) stabilization of Cu2+-Cu+ and Cu+-Cu0 redox pairs where the electron transfer is facilitated by zirconia support and (iii) assisting the recombination and release of hydrogen during the transformation of produced on zirconia surface intermediates.

Transition metal modified activated carbons from biomass and coal treatment products as catalysts for methanol decomposition

Copper, iron and cobalt supported on activated carbon materials are compared as catalysts in methanol decomposition in view of their potential application as intelligent carriers of hydrogen. The activated carbon supports were obtained from renewable agriculture waste (peach shell) or coal treatment by-products (coal tar pitch). The parent activated carbons and their transition metal modifications were characterized by nitrogen physisorption, XRD, UV–Vis, FTIR, Mossbauer spectroscopy and TPR in hydrogen, and the surface functional groups were determined by the Bohm method. It was assumed that the formation of transition metal modified activated carbon catalysts is a complex process which proceeds during the preparation procedure with the activity of the support and also during the catalysis by the influence of the reaction medium. The decisive effect of carbon basal planes over the texture and surface functionality of the support on the formation of transition metals active phase was assumed. Among the studied materials, cobalt modifications exhibited excellent catalytic activity and selectivity in methanol decomposition to H2 and CO despite the nature of the activated carbons used.

Spark plasma sintering synthesis of Ni1−xZnxFe2O4 ferrites: Mössbauer and catalytic study

Nickel-zinc ferrite nanoparticles, Ni1−xZnxFe2O4 (x = 0, 0.2, 0.5, 0.8, 1.0) were prepared by combination of chemical precipitation and spark plasma sintering (SPS) techniques and conventional thermal treatment of the obtained precursors. The phase composition and structural properties of the obtained materials were investigated by X-ray diffraction and Mössbauer spectroscopy and their catalytic activity in methanol decomposition was tested. A strong effect of reaction medium leading to the transformation of ferrites to a complex mixture of different iron containing phases was detected. A tendency of formation of Fe-carbide was found for the samples synthesized by SPS, while predominantly iron-nickel alloys ware registered in TS obtained samples. The catalytic activity and selectivity in methanol decomposition to CO and methane depended on the current phase composition of the obtained ferrites, which was formed by the influence of the reaction medium.

Critical evaluation of the state of iron oxide nanoparticles on different mesoporous silicas prepared by an impregnation method

Mesoporous SBA-15 (space group p6 mm), KIT-6 ( Ia3 d) and KIT-5 ( Fm3 m) silicas, exhibiting different 2-D and 3-D channel- or cage-like pore structure and pore dimensions have been used as supports for iron oxide nanoparticles. The iron modification of the silica was performed according to a frequently used impregnation technique from aqueous iron nitrate solution. The materials were characterized by nitrogen physisorption, X-ray diffraction, TEM–EDX, Moessbauer spectroscopy, and temperature-programmed reduction (TPR) and tested in the catalytic decomposition of methanol. It is established that the location and dispersion of iron oxide nanoparticles are affected by the pore topology of the support. The most homogeneously dispersed iron oxide nanoparticles are observed using silica host matrix exhibiting a 3-D channel-like structure and pore diameters about 7 nm, and the thus-obtained composites exhibit high catalytic activity and selectivity in methanol decomposition to CO and hydrogen. For all the samples, characterized with a low mesopore volume and small pore diameters/pore entrances, the formation of larger iron oxide particles, mainly located on the outer surface, is observed. Inhomogeneously dispersed iron oxide particles with a large fraction of isolated, strongly interacting with the support, iron species, and possessing low catalytic activity and usually high selectivity to methane, are found for the silicas with relatively larger pores/pore entrances.

Synthesis, characterization and catalytic properties of nanodimensional nickel ferrite/silica composites

Nanosized nickel ferrite/silica composites are synthesized using the sol–gel method. X-rays diffraction, Mössbauer and infrared spectroscopies, magnetic measurements and thermo-programmed reduction with hydrogen are used for their characterization. Significant differences in their catalytic activity and selectivity in methanol decomposition to CO and methane, depending on the ferrite/silica ratio, the annealing temperature and the phase transformations of the samples by the reaction medium are observed.

Catalytic Properties of Ni3Al Foils for Methanol Decomposition

Hydrogen was produced by methanol decomposition over cold-rolled foils of intermetallic compound Ni3Al which is known as an excellent high-temperature structural material. We found high catalytic activity and selectivity for methanol decomposition in flat cold-rolled Ni3Al foils. The catalytic activity was enhanced above 713 K by the spontaneous formation of fine Ni particles dispersed on carbon nanofibers during the reaction, resulting in high catalytic performance. The results demonstrate that the Ni3Al foils can be used both as catalyst precursors and as structural materials of microreactors for hydrogen production.

Characterization and Catalytic Properties of Ni3Al for Hydrogen Production from Methanol

ABSTRACTThe stability of catalytic activity and selectivity of Ni3Al for methanol decomposition were studied by life test at 633 K on the alkali-leached powder samples. The characterization of the samples was carried out by X-ray diffraction, inductively coupled plasma (ICP) analysis, SEM observation, and surface area measurement. The life test showed that the alkali-leached Ni3Al exhibits a very stable activity and a high selectivity for methanol decomposition. The surface characterization after reaction suggests that the high selectivity and stable activity may be attributed to the formation of tiny particles and porous structure which increased the surface area significantly during reaction. These results indicate a possibility of Ni3Al as a catalyst for hydrogen production reaction.

Characterization of Wall-Type Nickel Catalysts for Methanol Decomposition, Prepared on an Aluminum Plate by Electroless Plating

Various wall-type nickel catalysts were prepared on aluminum plates by electroless plating under changing conditions for displacement plating of zinc and chemical reduction plating of nickel, and their physicochemical properties were investigated. Correlation between these physicochemical properties and the decomposition properties of methanol over these plated catalysts was examined. The results show that the decomposition performance of the plated catalysts does not correlate with the surface areas of the plated layer but depends on the ratio of the crystallite size of nickel particles, as determined by XRD, to that of aluminum particles. This finding suggests the involvement in catalytic activity of aluminum that dissolves from the substrate in the plated layer as well as nickel, which is considered as the active site.Elemental component analysis and elemental state analysis in the plated layer indicate that the use of sodium hypophosphite monohydrate as a reducing agent results in the incorporation of phosphorus in the plated layer, and the plated catalyst with high selectivity of carbon monoxide and hydrogen for methanol decomposition contains large amounts of zinc and phosphorus, and a small amount of aluminum, with nickel in the bulk layer of this catalyst being in a metallic-state. The finding in which granular Ni3P and Ni/ZnO catalysts, with high selectivity for methanol decomposition, had metallic-state nickel suggests that some incorporation of phosphorus and zinc oxide, that increased the metallic-state of nickel, and the small amount of aluminum in the plated layer produce the high selectivity for methanol decomposition.

Synergistic promotion of CeO 2 and La 2O 3 in Pd/Al 2O 3 catalysts for methanol decomposition

A series of Pd catalyst supported by CeO 2 and La 2O 3-modified γ-Al 2O 3 was prepared for methanol decomposition. The BET surface area was obtained by N 2-adsorption. FTIR was used to obtain information of CO adsorbed on the reduced catalysts. A synergistic effect between CeO 2 and La 2O 3 on γ-Al 2O 3 was observed for promoting the catalytic properties of Pd, which resulted in high activity and selectivity for methanol decomposition into CO and H 2.

Methanol Decomposition on Fe2O3 /MCM-48 Silica Catalyst

Fe2O3/MCM-48 silica samples are characterized by high catalytic activity and methane selectivity in methanol decomposition. The catalytically active phase is substantially changed by the reaction medium and/or hydrogen pretreatment.

Evaluation of the Selectivity for Methanol Decomposition over Anodized Aluminum Plate Catalyst Coated with Silica.

A plate type methanol decomposition catalyst which has higher heat conductivity was prepared based on anodic oxidation of aluminum. In order to reduce the formation of dimethyl ether as a by-product at the acid site of alumina, silica was coated on the anodized alumina plate. By the measurement of ammonia TPD, it was found that the acidity of the silica coated catalyst was lower than that of the plate without coating. As for the silica coated plate, the profile of methanol TPD also showed that the formation of dimethyl ether was smaller and peak temperature was higher, although those without silica coating indicated a large amount of dimethyl ether formation. After Pd was loaded on the plate, the catalytic activity of methanol decomposition to hydrogen and carbon monoxide and the formation of dimethyl ether as a by-product were evaluated at 200 and 250°C by a continuous fixed bed reactor. The content and dispersion of Pd of silica coated catalysts were smaller than that of the hydrated catalyst without silica coating and the formation rate of carbon monoxide was increased with increasing metal surface area of Pd. The formation rate of dimethyl ether over the silica coated catalyst was approximately 1/20 of that of the catalyst without silica coating and it was independent of silica contents.