Selective Catalytic Reduction of NO by C3H6 over Co/Al2O3 Catalyst with Extremely Low Cobalt Loading

In order to reveal the optimum Co loading, the selective catalytic reduction of NO with C₃H₆ over Co/Al₂O₃ catalyst was studied in a systematic fashion by varying the amount of cobalt oxide. It was found that upon loading a small amount of cobalt oxide (namely 0.5 wt% on a Co metal basis), the combination between Co(II) acetate salt and a high-purity alumina provided an active catalyst in the presence of excess oxygen and water. TPR measurement showed the presence of Co species other than CoAl₂O₄ spinel in the most excellent performance catalyst, from which the active sites should be produced.     

Methane oxidative coupling over Na2WO4/SiO2

Methane oxidative coupling (MOC) was studied over Na₂WO₄/SiO₂. The effect of Na₂WO₄ loading and reaction conditions on the catalytic behaviour was investigated. XRD, SEM, LRS and XPS have been used to study the catalyst morphology, Na₂WO₄ dispersity and surface oxygen species. These results were correlated with the catalytic activity and selectivity.     

Na2WO4/Co–Mn/SiO2 Catalyst for the Simultaneous Production of Ethylene and Syngas from CH4

Na₂WO₄/Co–Mn/SiO₂ catalyst was prepared and used for the simultaneous production of ethylene and syngas from CH₄. A CH₄ conversion of 38% and a yield of 21% for (C₂H₄ + CO), with a C₂H₄/CO/H₂ ratio of 1/0.7/0.7 were obtained under the optimized conditions.     

The Effects of CO2 and H2O on the NO x Destruction Performance of a Model NO x Storage/Reduction Catalyst

The effects of CO₂ and H₂O on the NO _x storage and reduction characteristics of a Pt/Ba/Al₂O₃ catalyst were investigated. The presence of CO₂ and H₂O, individually or together, affect the performance and therefore the chemistry that occurs at the catalyst surface. The effects of CO₂ were observed in both the trapping and reduction phases of the experiments, whereas the effect of H₂O seems limited to the trapping phase. The data also indicate that multiple types of sorption sites (or mechanisms for sorption) exist on the catalyst. One mechanism is characterized by a rapid and complete uptake of NO _x . A second mechanism is characterized by a slower rate of NO _x uptake, but this mechanism is active for a longer time period. As the temperature is increased, the effect of H₂O decreases compared to that of CO₂. At the highest temperatures examined, the elimination of H₂O when CO₂ is present did not affect the performance.     

Selective Reduction of NO with CO Over Titania Supported Transition Metal Oxide Catalysts

A series of transition metal oxides promoted titania catalysts (MO _x /TiO₂; M = Cr, Mn, Fe, Ni, Cu) were prepared by wet impregnation method using dilute solutions of metal nitrate precursors. The catalytic activity of these materials was evaluated for the selective catalytic reduction (SCR) of NO with CO as reductant in the presence of excess oxygen (2 vol.%). Among various promoted oxides, the MnO _x /TiO₂ system showed very promising catalytic activity for NO + CO reaction, giving higher than 90% NO conversion over a wide temperature window and at high space velocity (GHSV) of 50,000 h⁻¹. It is remarkable to note that the catalytic activity increased with oxygen, up to 4 vol.%, under these conditions leading primarily to nitrogen. Our TPR studies revealed the presence of mixed oxidation states of manganese on the catalyst surface. Characterization results indicated that the surface manganese oxide phase and the redox properties of the catalyst play an important role in final catalytic activity.     

CO2 reforming of methane over vanadia-promoted Rh/SiO2 catalysts

The reforming of methane with carbon dioxide over rhodium dispersed on silica, Rh/SiO₂, and vanadia-promoted silica, Rh/VO_x/SiO₂, was studied by kinetic test reactions under differential conditions in a temperature range from 723 to 773 K. Transmission infrared spectroscopy was applied to observe the interaction of CO₂ with the catalysts and the formation of surface intermediates during the CO₂–CH₄ reforming reaction. To analyze carbon deposition XP spectroscopy and TPO was carried out. It has been shown that the promotion of Rh/SiO₂ catalysts with vanadium oxide enhances the catalytic activity for CO₂ reforming of methane and decreases the deactivation by carbon deposition. This is attributed to the formation of a partial VO_x overlayer on the Rh surface, which reduces the size of accessible ensembles of Rh atoms required for coke formation and creates new sites at the Rh–VO_x interfacial region that are considered to be active sites for the activation/dissociation of carbon dioxide. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ir/H-ZSM-5 Catalysts in the Selective Reduction of NOx with Hydrocarbons

Three different Ir catalysts supported on H-ZSM-5 were prepared and tested for the selective catalytic reduction of NO under net oxidizing conditions using propene as reducing agent. The preparation of highly active Ir catalysts and the elaboration of a procedure for enhancing activity by on stream conditioning was targeted. Structural changes of the catalyst during conditioning were investigated by means of XRD, TEM and activity measurements. Under reaction conditions Ir was present as Ir⁰ and IrO₂. The presence of Ir⁰ was essential for high DeNOx activity. The ratio of Ir⁰/Ir⁴⁺ was found to depend on the size of Ir-containing crystallites. Larger crystallites contained predominantly Ir⁰. Crystallite size and oxidation state of Ir have been identified to be crucial for the NO reduction behaviour of Ir/H-ZSM-5.     

Promoting Effect of Pt Addition to V2O5/ZrO2 Catalyst on Reduction of NO by C3H6

The effect of Pt addition to a V₂O₅/ZrO₂ catalyst on the reduction of NO by C₃H₆ has been studied by FTIR spectroscopy as well as by analysis of the reaction products. Pt loading promoted the catalytic activity remarkably. FTIR spectra of NO adsorbed on the catalysts doped with Pt show the presence of two different types of Pt sites, Pt oxide and Pt cluster, on the surface. The amount of these sites depends on Pt contents and the catalyst state. Pt atoms highly disperse on the surface as Pt oxide at low Pt content, being aggregated into Pt metal clusters by increasing Pt amount or reducing the catalysts. The spectral behavior of V=O bands on the surface also supports the formation of Pt clusters. It is concluded that Pt promotes the NO–C₃H₆ reaction through a reduction–oxidation cycle between its oxide and cluster form.     

CO hydrogenation over a RhVO4/SiO2 catalyst after H2 reduction

The hydrogenation of CO over a RhVO₄/SiO₂ catalyst has been investigated after H₂ reduction at 773 K. A strong metal–oxide interaction (SMOI) induced by the decomposition of RhVO₄ in H₂ enhanced not only the selectivity to C₂ oxygenates but also the CO conversion drastically, compared with an unpromoted Rh/SiO₂ catalyst. The selectivity of the RhVO₄/SiO₂ catalyst was similar to those of conventional V₂O₅‐promoted Rh/SiO₂ catalysts (V₂O₅–Rh/SiO₂), but the CO dissociation activity (and TOF) was much higher than for V₂O₅–Rh/SiO₂, and hence the yield of C₂ oxygenates was increased. This revised version was published online in July 2006 with corrections to the Cover Date.     

Simultaneous Production of Syngas and Ethylene from Methane by Combining its Catalytic Oxidative Coupling over Mn/Na2WO4/SiO2 with Gas Phase Partial Oxidation

A new route of methane utilization is presented, in which methane is converted to H₂, CO and C₂H₄ simultaneously with equal mole ratio, in order that the produced mixture could be used in the synthesis of propanal via hydroformylation. Kinetically controlled free radical gas phase methane oxidation was combined with its catalytic oxidative coupling over Mn/Na₂WO₄/SiO₂ to concomitantly acquire ethylene and syngas with close concentration. Under the optimal reaction condition, a mole ratio of CO:H₂:C₂H₄=1.0:1:0.9 was obtained with a yield of 11.6% and a selectivity of 68% to the target products based on C, while the selectivity to CO₂ is as low as 18.1%.     

The oxidative dehydrogenation of ethane with CO2 over Mo2C/SiO2 catalyst

Mo₂C prepared on SiO₂ was found to be an effective catalyst for the dehydrogenation of ethane to produce ethylene in the presence of CO₂. The selectivity to ethylene at 850–923 K was 90–95% at an ethane conversion of 8–30%. With the increase of the temperature the dry reforming of ethane became also a significant process. It is assumed that the Mo oxycarbide formed in the reaction between CO₂ and Mo₂C plays an important role in the activation of ethane. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electrochemically Assisted Photocatalysis of Hybrid WO3/TiO2 Films: Effect of the WO3 Structures on Charge Separation Behavior

In this study, the photocatalysis of hybrid WO₃/TiO₂ films with different loadings of WO₃ were investigated with and without potential bias. It was clearly indicated that hybrid WO₃/TiO₂ films show less photo-reactivity under only UV-irradiation, while more effective photocatalysis under potential bias than either TiO₂ or WO₃ by themselves, their photocatalytic performance depending on the loadings of WO₃. In particular, a hybrid WO₃/TiO₂ film involving an amorphous-like WO₃ phase plays a significant role in an enhancement of the electrochemically assisted photocatalysis.     

Selective Catalytic Reduction of NOx with CH4 over the In/Sulfated TiO2 Catalyst

Tungstated TiO₂ (WTi), tungstated Fe₂O₃ (WFe), tungstated SnO₂ (WSn), sulfated TiO₂ (STi), sulfated Fe₂O₃ (SFe), and sulfated SnO₂ (SSn) are used as the support for the In and Pd catalysts for the SCR of NO with methane. It was found that the In/STi catalyst with a 2% indium loading showed the highest NO_x conversion (39% at 450 °C and 12,000 h⁻¹) among all of the catalysts studied. The acid strength of the STi support was very important for the formation of the InO⁺ site, which was thought to be the active site for NO reduction. The activity of the In/STi catalyst can be improved by increasing the surface area of the STi support. The most attractive feature of the In/STi catalyst is its high resistance for SO₂.     

Catalytic hydrolysis of chlorofluorocarbon (CFC-12) over WO3/ZrO2

The catalytic decomposition of CFC-12 (CCl₂F₂) in the presence of water vapor was investigated over a series of solid acids WO₃/ZrO₂. Compared with tungstic acid, ammonium metatungstate is a better source of tungsten oxide for the preparation of WO₃/ZrO₂ catalysts. CFC-12 decomposition activities of WO₃/ZrO₂ catalysts are in good agreement with their acidities. Enhancing the acidities of catalysts is favorable to increase their CFC-12 decomposition activities. WO₃/ZrO₂ catalysts calcined at higher temperature exhibit good catalytic activity and stability for the hydrolysis of CFC-12, and show better structural stability during the reaction.     

Infrared Study of Benzene Hydrogenation on Pt/SiO2 Catalyst by Co-adsorption of CO and Benzene

FT-IR spectra of the co-adsorption of benzene and CO have been performed to identify the preferred adsorption sites of hydrogen and benzene on a Pt/SiO₂ catalyst for hydrogenation of benzene. Results of CO adsorbed on atop sites on Pt/SiO₂ includes: an α peak at 2091 cm⁻¹, a β peak at 2080 cm⁻¹ and a γ peak at 2067 cm⁻¹ indicating three kinds of adsorption sites for dissociative hydrogen on Pt/SiO₂. The site of lowest CO stretching frequency offers stronger adsorbates–metal interaction for benzene and hydrogen. Hydrogen binding on the site of lowest CO stretching frequency before benzene adsorption significantly enhances the reaction rate of benzene hydrogenation.     

Photo-electrochemical properties of amorphous WO3 supported on TiO2 hybrid catalysts

In this work, we have carried out ivestigations on photo-electrochemical energy conversion and storage on WO₃/TiO₂ hybrid materials. The band gap excitation of the hybrid WO₃/TiO₂ having an amorphous WO₃ phase led to an effective photo-charging to form a tungsten bronze structure by the intercalation of protons while a reversible discharging through de-intercalation could also be observed.     

A TPD study of H2 ON Ru/SiO2 and Ru-Cu/SiO2

In H₂ TPD from Ru/SiO₂, two desorption peaks were observed. Both exchanged H for D in sequential dosing experiments. These hydrogen adsorption states were also found for Ru-Cu/SiO₂, along with another, higher temperature state at 400–500 K. This last state was neither exchangeable with nor replaceable by deuterium subsequently dosed at 150 K. The three chemisorption states are attributed to hydrogen held at the interface between Ru and SiO₂ (< 300 K), adsorbed on Ru particles (310–380 K), and held at the Ru-Cu interface (> 400 K).     

Effect of chlorine on Ir/CeO2 catalyst behavior for preferential CO oxidation

Effect of chlorine on Ir/CeO₂ catalyst behavior for preferential CO oxidation is investigated by high-resolution transmission electron microscopy, X-ray photoemission spectroscopy, and diffuse reflectance infrared spectroscopy. The presence of chlorine favors the dispersion of Ir particles. On ceria support, the replacement of the lattice oxygen by chloride ions would produce CeOCl species, which could hinder the formation of hydroxyl groups and carbonate and/or carboxylate species on the ceria surface. These features could explain the decreased activity of the Cl-containing Ir/CeO₂ sample.     

NO2 Reduction with Nitromethane over Ag/Y: A Catalyst with High Activity over a Wide Temperature Range

Nitromethane (NM) is a very efficient reductant for converting NO₂ to N₂ over Ag/Y: Between 140 °C and 400 °C, the N₂ yield is close to 100%. This high N₂ yield results from the ability of Ag/Y to effectively catalyze the reaction between NM and NO₂. This high catalytic activity of Ag/Y is minimally affected by surface bound CN⁻, NC⁻, or acetate, all of which are stable at temperatures below ∼300 °C. At T ≥ 400 °C, there is a reaction path that yields N₂ from NM even in the absence of NO₂. However even at 400 °C, under typical deNO _x conditions, most N₂ molecules are formed as a result of the reaction of NM and NO₂.     

Formation of active sites on Ir/WO3–SiO2 for selective catalytic reduction of NO by CO

Pretreatment conditions for the activation of Ir/WO₃–SiO₂ for the selective catalytic reduction of NO by CO in the presence of excess O₂ were studied. Sequential treatment involving calcination in the presence of O₂ and H₂O followed by reduction and then re-oxidation under mild conditions was found to effectively activate Ir/WO₃–SiO₂. Temperature-programmed desorption during calcination, X-ray diffraction, and temperature-programmed reduction by H₂ revealed that calcination was necessary for oxidative removal of the NH₃ ligands from the iridium precursor, that reduction produced metallic iridium and partially reduced tungsten oxide, and that re-oxidation produced tungsten oxide with low reducibility. Transmission electron microscopy revealed that Ir was supported on finely dispersed tungsten oxide and that the iridium particle size after the sequential activation was 1–1.5 nm.