Applied Catalysis B, Environmental (v.55, #4)
Production of hydrogen by oxidative reforming of ethanol over Pt catalysts supported on Al2O3 modified with Ce and La by R.M. Navarro; M.C. Álvarez-Galván; M. Cruz Sánchez-Sánchez; F. Rosa; J.L.G. Fierro (229-241).
A series of Pt catalysts supported on alumina modified by Ce and/or La were prepared and tested in the reaction involving the production of hydrogen by oxidative reforming of ethanol. Characterization of the catalysts by N2 adsorption, X-ray diffraction, TPR and X-ray photoelectron spectroscopy (XPS) revealed differences in the interaction between platinum and the supports. These differences have important implications in the behaviour of the catalysts for the ethanol-reforming reaction. Ethanol conversion on the Pt/(La)Al2O3 catalyst was found to be close to that of the Pt/Al2O3 catalyst. However, modification of the Al2O3 substrate by ceria led to a more active Pt/(Ce)Al2O3 catalyst. A lower promotion effect was observed when both ceria and lanthana were present on the support substrate. TPR and XPS analyses of ceria-containing samples revealed the existence of a strong interaction between platinum and ceria. This interaction between Pt crystallites at the ceria surface seemed to be responsible for the better performance of the cerium-containing catalysts. It is suggested that the platinum–ceria interaction affects the adsorption–decomposition of ethanol to CH4 and CO products and their subsequent reforming reactions with steam. When both ceria and lanthana were present on the support substrate the platinum–ceria interaction was diminished, reducing the promoter effect in the production of hydrogen by oxidative reforming of ethanol.
Keywords: Platinum; Alumina; Ceria; Lanthana; Hydrogen production; Ethanol;
Preparation, characterization and photocatalytic activity of Si-doped and rare earth-doped TiO2 from mesoporous precursors by Xiaoli Yan; Jing He; David G. Evans; Xue Duan; Yuexiang Zhu (243-252).
Si-doped and rare earth-doped TiO2 with large specific surface area were prepared by the hydrothermal method and sol–gel route, respectively, using C18H37NH2 as template. The samples were characterized by XRD, FT-IR, low-temperature N2 adsorption–desorption measurement, XPS and solid state UV–vis diffuse reflectance spectroscopy. The pore size for Si-doped TiO2 exhibits both mesoporous and microporous distribution, and that for rare earth-doped TiO2 exhibits a sharp and narrow distribution in microporous range. The photocatalytic activities were investigated with the degradation of phenol as probe reaction. Compared with pure TiO2, the conversion of phenol and selectivity to CO2 increases when adding rare earth elements, and the substitution of Si for Ti in an appropriate range also increases the conversion of phenol.
Keywords: Si-doped TiO2; Rare earth-doped TiO2; Mesoporous precursors; Photocatalytic activity;
Effect of TiO2 thin film thickness and specific surface area by low-pressure metal–organic chemical vapor deposition on photocatalytic activities by Sang-Chul Jung; Sun-Jae Kim; Nobuyuki Imaishi; Yong-Ick Cho (253-257).
TiO2 photocatalyst films having an anatase crystal structure with different thickness were prepared by the low-pressure metal–organic chemical vapor deposition (LPMOCVD) to examine the effect of growth conditions on photocatalytic activity. Film thickness was linearly proportional to the deposition time. Structure of the film was strongly dependent on the deposition time. In early stage of deposition, fine particles deposit on the substrate. As increasing the deposition time, crystal orientation is gradually selected following the Kolmogorov model and c-axis oriented columnar crystals become dominant. The photocatalytic activity strongly depends on the film deposition time (or film thickness) in nonlinear way. The optimum thickness of TiO2 catalyst film grown by LPMOCVD may locate between 3 and 5 μm.
Keywords: TiO2 thin film; Low-pressure metal–organic chemical vapor deposition; Photocatalytic activity; Film thickness; Specific surface area;
Comparison of activities in selective catalytic reduction of NO x by C3H8 over Co/MFI, Fe/MFI, and H/MFI zeolite catalysts by Hiroto Imai; Toshiyuki Ogawa; Kazuo Sugimoto; Masakazu Kataoka; Yumo Tanaka; Takehiko Ono (259-265).
The Co/MFI(SiO2/Al2O3 = 30) were prepared by a precipitation method with NaOCl in alkali solutions exhibited high activities to N2 at 250 °C for the selective catalytic reduction (SCR) of NO x . These catalysts showed two UV–vis bands at 700 and 400 nm, indicating the presence of octahedral Co(III) as well as tetrahedral Co(II). The high SCR activity over such Co(III, II)/MFI(30) seems to come from Co(III)O moieties. The Co(II)MFI(30) catalysts prepared from Co(II)Cl2 exhibited low SCR activities due to the presence of tetrahedral Co(II) ions in MFI. Less CO formation occurred over Co/MFI catalysts. The Fe/MFI(30) catalyst exhibited high activity due to the presence of some FeO species in MFI but more amount of CO were produced during SCR. H/MFI(30) catalyst exhibited a good SCR activity. However, more amount of carbonaceous deposits were produced on it. The correlation between acid concentration and SCR activity was discussed over H/MFIs.
Keywords: SCR of NO x ; Co/MFI; C3H8; UV–vis spectra of Co(II) and Co(III);
Cobalt-, copper- and iron-containing monolithic aluminosilicate-supported preparations for selective catalytic reduction of NO with NH3 at low temperatures by M. Brandhorst; J. Zajac; D.J. Jones; J. Rozière; M. Womes; A. Jimenez-López; E. Rodríguez-Castellón (267-276).
Aluminium-doped mesoporous monolithic silica possessing fine mesopores has been prepared via the direct liquid crystal templating pathway using a non-ionic surfactant template and has been used as a support for cobalt-, copper-, and iron-based formulations in the selective catalytic reduction (SCR) of NO with ammonia in the presence of oxygen at low temperatures in the range of 373–723 K. The monolithic support was characterised by N2 gas adsorption at 77 K, powder X-ray diffraction (XRD) and NH3 adsorption at 373 K. Surface area, pore structure and surface acidity of the catalysts before and after being subjected to catalytic testing were determined, and good stability of pore structure and surface properties under SCR conditions was indicated. The NO conversions on aluminosilicate monolith-supported catalysts were compared with those observed on the reference catalyst, EUROCAT powder. The Co-functionalised catalysts appeared less relevant to DeNO x purposes. Two impregnated and two ion-exchanged catalysts containing copper and iron showed catalytic performance comparable to that of the reference catalyst. They produced only small amounts of undesired product N2O, the Fe-containing formulations being even more selective than EUROCAT. The nature of metal species in these catalysts was investigated with the aid of Cu 2p X-ray photoelectron spectroscopy (XPS) and 57Fe Mössbauer spectroscopy.
Keywords: Catalyst materials; Co-, Cu- and Fe-based monolithic aluminosilicate-supported preparations; SCR of NO with NH3;
Oxidation of ethanol over supported manganese catalysts—effect of the carrier by Janusz Trawczyński; Beata Bielak; Włodzimierz Miśta (277-285).
MnO x catalysts supported on alumina, titania or yttria-stabilised zirconia were studied in ethanol oxidation. Catalysts were characterized by determining their XRD, TPR, TPD-O2 and TPD-NH3 properties and light-off behavior. The effect of kind of carrier on activity in the ethanol oxidation and on selectivity to acetaldehyde (ACA) was determined. Relation between the TPR properties of the catalysts and their activity in ethanol conversion is suggested. The maximum of selectivity to ACA appears in the same sequence of temperatures as the first peak of oxygen desorption from supported MnO x catalysts.
Keywords: Manganese oxides; Carrier; Ethanol; Exhausts treatment;
In situ XPS investigations of Cu1−x Ni x ZnAl-mixed metal oxide catalysts used in the oxidative steam reforming of bio-ethanol by Subramani Velu; Kenzi Suzuki; Munusamy Vijayaraj; Sanmitra Barman; Chinnakonda S. Gopinath (287-299).
A series of CuNiZnAl-multicomponent mixed metal oxide catalysts with various Cu/Ni ratios were prepared by the thermal decomposition of Cu1−x Ni x ZnAl-hydrotalcite-like precursors and tested for oxidative steam reforming of bio-ethanol. Dehydrogenation of EtOH to CH3CHO is favored by Cu-rich catalyst. Introduction of Ni leads to C―C bond rupture and producing CO, CO2 and CH4. H2 yield (selectivity) varied between 2.6–3.0 mol/mol of ethanol converted (50–55%) for all catalysts at 300 °C. The above catalysts were subjected to in situ XPS studies to understand the nature of active species involved in the catalytic reaction. Core level and valence band XPS as well as Auger electron spectroscopy revealed the existence of Cu2+, Ni2+ and Zn2+ ions on calcined materials. Upon in situ reduction at reactions temperatures, the Cu2+ was fully reduced to Cu0, while Ni2+ and Zn2+ were partially reduced to Ni0 and Zn0, respectively. On reduction, the nature of ZnO on Cu-rich catalyst changes from crystalline to amorphous, relatively inert and highly stabilized electronically. Relative concentration of the Ni0 and Zn0 increases upon reduction with decreasing Cu-content. Valence band results demonstrated that the overlap between 3d bands of Cu and Ni was marginal on calcined materials, and no overlap due to metallic clusters formation after reduction. Nonetheless, the density of states at Fermi level increases dramatically for Ni-rich catalysts and likely this influences the product selectivity.
Keywords: Mixed metal oxides; Copper oxide; Nickel oxide; Hydrotalcite; Steam reforming; Oxidative steam reforming; Autothermal reforming; Bio-ethanol; XPS; Auger electron spectroscopy; Hydrogen; Fuel cell;
Catalytic decomposition of chlorodifluoromethane (HCFC-22) over platinum supported on TiO2–ZrO2 mixed oxides by Hongxia Zhang; Ching Fai Ng; Suk Yin Lai (301-307).
Sulfated and non-sulfated TiO2–ZrO2 were promoted with platinum and the activity and selectivity of the resulting catalysts for the hydrolytic decomposition chlorodifluoromethane in air was investigated. The addition of platinum reduced the specific surface area of the catalyst slightly and lowered the catalytic activity. On the other hand, the selectivity of the catalysts towards CO2 formation was much improved. Metallic platinum was formed by the reduction of the platinum precursor with carbon monoxide produced during the hydrolysis of chlorodifluoromethane over the acidic mixed oxide and promoted the oxidation of CO. At the same time, platinum suppressed completely the formation of the fluorinated byproduct CHF3, possibly by anchoring itself on the active sites responsible for the fluorination reaction. The platinum promoted non-sulfated TiO2–ZrO2 was stable and gave more than 90% of CHClF2 conversion and 95% selectivity to CO2 for over 60 h.
Keywords: Hydrochlorofluorocarbon destruction; Platinum catalysts; Titania–zirconia;
AUTHOR INDEX (311-312).
SUBJECT INDEX (313-317).
CONTENTS OF VOLUME (319-320).