Stable carbon dioxide reforming of methane over modified Ni/Al2O3 catalysts

CO₂ reforming of methane was studied over modified Ni/Al₂O₃ catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al₂O₃, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO₂ reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even in the absence of diluent gas and the activity changed only slightly during 100 h operation. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the development of metallic particles and their initial catalytic properties in the CO + H2 reaction over Co/Al2O3 catalyst

Formation of Co^o phases with different surface structure over 10 wt% Co/Al₂O₃ and their catalytic properties were induced by pretreatments in H₂ at 570 K for 1 h or 20 h. Electronic behaviour of the Co^o phase, which consists of small (after 1 h reduction) or large bulk-like particles (after 20 h reduction), did not change during the CO hydrogenation after 5 h on stream as was determined by XPS. On the basis of the measured C₂₊ hydrocarbon selectivities the CO molecules are suggested to dissociate on small Co particles to a larger extent than on large cobalt particles. The slight decrease in the catalytic activity with increasing time on stream obtained for the long-term reduced sample is explained by the change in the surface Co^o content detected by XPS. The increase in the catalytic activity along with the change in olefin selectivity, measured for the sample reduced for 1 h, is interpreted by the change of a reaction path involving the Co^o-support interface during the initial period of the reaction.     

Dehydrogenation of ethylbenzene to styrene over Fe2O3/Al2O3 catalysts in the presence of carbon dioxide

An Fe₂O₃ (10 wt%)/Al₂O₃ (90 wt%) catalyst prepared by a coprecipitation method was found to be effective for dehydrogenation of ethylbenzene to produce styrene in the presence of CO₂ instead of steam used in commercial processes. The dehydrogenation of ethylbenzene over the catalyst in the presence of CO₂ was considered to proceed both via a one-step pathway and via a two-step pathway. CO₂ was found to suppress the deactivation of the catalyst during the dehydrogenation of ethylbenzene. This revised version was published online in July 2006 with corrections to the Cover Date.     

Efficient production of hydrogen and multi-walled carbon nanotubes from ethanol over Fe/Al2O3 catalysts

Fe/Al₂O₃ catalysts with different Fe loadings (10-90 mol%) were prepared by hydrothermal method. Ethanol decomposition was studied over these Fe/Al₂O₃ catalysts at temperatures between 500 and 800 °C to produce hydrogen and multi-walled carbon nanotubes (MWCNTs) at the same time. The results showed that the catalytic activity and stability of Fe/Al₂O₃ depended strongly on the Fe loading and reaction temperature. The Fe(30 mol%)/Al₂O₃ and Fe(40 mol%)/Al₂O₃ were both the effective catalyst for ethanol decomposition into hydrogen and MWCNTs at 600 °C. Several reaction pathways were proposed to explain ethanol decomposition to produce hydrogen and carbon (including nanotube) at the same time.     

The positive effect of hydrogen on the reaction of nitric oxide with carbon monoxide over platinum and rhodium catalysts

The effect of adding 330–4930 ppm hydrogen to a reaction mixture of NO and CO (2000 ppm each) over platinum and rhodium catalysts has been investigated at temperatures around 200–250°C. Hydrogen causes large increases in the conversion of NO and, surprisingly, also of CO. Oxygen atoms from the additional NO converted are eventually combined with CO to give CO₂ rather than react with hydrogen to form water. This reaction is described by CO + NO +3/2H₂ CO₂ + NH₃ and accounts for 50–100% of the CO₂ formed with Pt/Al₂O₃ and 20–50% with Rh/Al₂O₃. With the latter catalyst a substantial amount of NO converted produces nitrous oxide. Comparison with a known study of unsupported noble metals suggests that isocyanic acid (HNCO) might be an important intermediate in a reaction system with NO, CO and H₂ present.     

Promoting effect of NiAl2O4 for supported Ni particles on sprayed Ni/Al2O3 catalysts

Ni/Al₂O₃ catalysts were prepared by the spray reaction method. The NiO particles supported on NiAl₂O₄ were stabilized against the aggregation and converted into smaller Ni particles by H₂ reduction. The Ni particles stabilized on NiAl₂O₄ marked anomalous high activity for CO hydrogenation, due to the stronger interaction between Ni and NiAl₂O₄. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Low-temperature water-gas shift reaction over Mn-promoted Cu/Al2O3 catalysts

Water-gas-shift reaction was carried our over a series of Mn-promoted Cu/Al₂O₃ catalysts in the temperature range of 448–533 K. The catalysts were characterized suitably by various techniques. The catalyst containing 8.55 wt% Mn was found to be the most active one among five catalysts tested. A maximum CO conversion of 90% was obtained over this catalyst at 513 K with a CO space-time of 5.33 h. The catalysts were found to be structure sensitive for the low-temperature water-gas shift reaction. A detailed kinetic study was performed for the reaction under investigation over the best catalyst. The kinetic data were fitted to two different models and the redox model was found to the better one than the other. From the estimated kinetic constant, the activation energy was determined to be 81 kJ/mol for the water-gas shift reaction in the temperature range of 448–463 K.     

The effect of phosphorus on the HDN reaction of piperidine,decahydroquinoline and ortho-propylaniline over Ni-MoS2/Al2O3 catalysts

The hydrodenitrogenation (HDN) of piperidine, decahydroquinoline (DHQ) and orthopropylaniline (OPA) has been studied over NiMo(P)/Al₂O₃ catalysts at 593 K and 3.0 MPa in order to understand the effect of phosphorus on the elementary HDN reaction steps. Phosphorus exhibited a negative effect on the HDN of piperidine and DHQ, both on the C-N bond cleavage reaction and on the subsequent hydrogenation reaction of alkene to alkane. A P/Al₂O₃ catalyst showed no HDN activity at all, neither with piperidine, nor with DHQ. A positive effect of phosphorus was observed in the HDN of OPA, where hydrogenation of the aromatic ring is needed and is rate limiting. It is suggested that introduction of phosphorus to NiMo/Al₂O₃ catalysts on the one hand decreases the available support surface area, and as a consequence the dispersion of the Ni-Mo-S phase and thus the capacity for C-N bond breaking and olefin hydrogenation. On the other hand, phosphorus induces either new or more active sites for the hydrogenation of aromatics.     

Effects of space velocity on methanol synthesis from Co2/Co/H2 over Cu/ZnO/Al2O3 catalyst

The space velocity had profound and complicated effects on methanol synthesis from CO₂/CO/H₂ over Cu/ZnO/Al₂O₃ at 523 K and 3.0MPa. At high space velocities, methanol yields as well as the rate of methanol production increased continuously with increasing CO₂ concentration in the feed. Below a certain space velocity, methanol yields and reaction rates showed a maximum at CO₂ concentration of 5–10%. Different coverages of surface reaction intermediates on copper appeared to be responsible for this phenomenon. The space velocity that gave the maximal rate of methanol production also depended on the feed composition. Higher space velocity yielded higher rates for CO₂/ H₂ and the opposite effect was observed for the CO/H₂ feed. For CO₂/CO/H₂ feed, an optimal space velocity existed for obtaining the maximal rate.     

Non-oxidative methane transformations into higher hydrocarbons over bimetallic Pt–Co catalysts supported on Al2O3 and NaY

The methane conversion under non-oxidative conditions over Al₂O₃ and NaY supported cobalt, platinum and Pt–Co bimetallic catalysts in a flow system has been investigated. The two-step process was applied in the temperature range between 523 and 673 K and 1 bar pressure and the one-step process was carried out under the conditions of 1073 K and 10 bar pressure. Addition of platinum to NaY and alumina supported cobalt samples results in the formation of metallic Co particles and Pt–Co bimetallic particles. On bimetallic catalysts in the two-step process, the amount of C₂₊ products formed were higher than that on mono-metallic samples. The synergism shown by the bimetallic system can be explained by: (i) enhanced reducibility of cobalt, and (ii) the co-operation of two types of active components (Co facilitates the chain-growth of partially dehydrogenated species produced on Pt in Pt–Co bimetallic particles). The use of higher pressures and high temperature makes it possible to run the process to form primarily ethane (and ethylene) which is predicted from thermodynamic calculations. For NaY as support, significantly enhanced activity and C₂₊ selectivity are obtained compared with Al₂O₃ as support, which can be attributed to the structural differences of metal particles (location, dispersion and reducibility).     

Reduction of lean NOx by ethanol over Ag/Al2O3 catalysts in the presence of H2O and SO2

The reduction of lean NOx using ethanol in simulated diesel engine exhaust was carried out over Ag/Al₂O₃ catalysts in the presence of H₂O and SO₂. The Ag/Al₂O₃ catalysts are highly active for the reduction of lean NOx by ethanol but the reaction is accompanied by side reactions to form CH₃CHO, CO along with small amounts of hydrocarbons (C₃H₆, C₂H₄, C₂H₂ and CH₄) and nitrogen compounds such as NH₃ and N₂O. The presence of H₂O enhances the NOx reduction while SO₂ suppresses the reduction. The presence of SO₂ along with H₂O suppresses the formation of acetaldehyde and NH₃. By infrared spectroscopy, it was revealed that the reactivity of NCO species formed in the course of the reaction was greatly enhanced in the presence of H₂O. The NCO species readily reacts with NO in the presence of O₂ and H₂O at room temperature, being converted to N₂ and CO₂ (CO). Addition of SO₂ suppresses the formation of NCO species and lowers the reactivity of the NCO species. However, the reduction of NOx is still kept at high conversion levels in the presence of H₂O and SO₂ over the present catalysts. About 80% of NOx in the simulated diesel engine exhaust was removed at 743 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Activity and stability of Cu/ZnO/Al2O3 catalyst promoted with B2O3 for methanol synthesis

The addition of B₂O₃ to a Cu/ZnO/Al₂O₃ catalyst increased the activity of the catalyst for methanol synthesis after an induction period during the reaction. The stability of the B₂O₃-containing Cu/ZnO/Al₂O₃ catalyst was greatly improved by the addition of a small amount of colloidal silica to the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gold supported CeO2/Al2O3 catalysts for CO oxidation: influence of the ceria phase

A series of low loading gold supported ceria/alumina catalysts have been prepared by the deposition–precipitation method, varying the pH of the synthesis. The catalysts were characterised by means of XRD, TEM, S_BET, XRF and UV–Vis techniques, and their catalytic activity towards CO oxidation in the absence and in presence of water in the stream, were tested. It has been found that in this low loading gold catalysts, where the metallic particles are far away one from another and the oxygen transportation is not the limiting step of the reaction, the electronic properties of the ceria phase and the structure of the metal-support perimeter more than the diameter of the gold nanoparticles is the determinant factor in the catalytic performances of the solid.     

Surface acidity investigation of A12O3 supports and Ni-Mo/Al2O3 catalysts using the temperature-programmed desorption oftert-butylamine

The relative acid site densities of a range of Ni-Mo/Al₂O₃ based catalysts were measured by the temperature-programmed desorption of tert-butylamine. The catalysts investigated possessed different surface areas and active species loadings. The effect of active species impregnation on the acidity of blank aluminas was also determined. Similarly the effect of sulphiding on catalyst acidity was also addressed.     

Pulse studies of CH4 interaction with NiO/Al2O3 catalysts

Pulse studies of the interaction of CH₄ and NiO/Al₂O₃ catalysts at 500°C indicate that CH₄ adsorption on reduced nickel sites is a key step for CH₄ oxidative conversion. On an oxygen-rich surface, CH₄ conversion is low and the selectivity of CO₂ is higher than that of CO. With the consumption of surface oxygen, CO selectivity increases while the CO₂ selectivity falls. The conversion of CH₄ is small at 500°C when a pulse of CH₄/O₂ (CH₄O₂=21) is introduced to the partially reduced catalyst, indicating that CH₄ and O₂ adsorption are competitive steps and the adsorption of O₂ is more favorable than CH₄ adsorption     

High performances of Pt-K/Al2O3 versus Pt-Ba/Al2O3 LNT catalysts in the simultaneous removal of NO x and soot

The potentiality of a Pt-K/Al₂O₃ catalyst in the simultaneous removal of particulate matter (soot) and NO _x is investigated in this work by means of Temperature Programmed Oxidation (TPO) experiments and Transient Response Method (TRM), and compared with Pt-Ba/Al₂O₃. The results point out the higher performances of K-based sample in the soot combustion as compared to the Ba-based catalyst, and similar behaviour in the NO _x -storage.     

Metal oxide catalysts for DME steam reforming: Ga2O3 and Ga2O3–Al2O3 catalysts

The steam reforming of dimethyl ether (DME) was performed on Ga₂O₃–Al₂O₃ mixed oxides prepared by sol–gel method. Ga₂O₃ significantly affects the catalytic performance with respect to the DME conversion and H₂ yield. The catalytic activity increases with the Ga concentration in Ga₂O₃–Al₂O₃ mixed oxides. It is very interesting that without the aid of an additional transition metal component, Ga₂O₃ and Ga₂O₃ containing Al₂O₃ mixed oxide system exhibit good activity in the reforming reaction. To the best of our knowledge, this is the first report that reveals the reforming ability of Ga₂O₃ for the production of H₂ from DME and/or methanol.     

Highly hydrogen-deficient hydrocarbon species for the CO2-reforming of CH4 on Co/Al2O3 catalyst

The dynamics of produced CO and H₂, measured by pulse surface reaction rate analysis (PSRA), revealed that the intermediate hydrocarbon species for the CO₂-reforming of CH₄ was highly hydrogen-deficient (CH_0.75) on supported Co/Al₂O₃ catalyst. It was also found that the species was more reactive than the less hydrogen-deficient one (CH_2.4) on Ni/Al₂O₃ catalyst.     

Deposition of CoO onto MoO3/Al2O3 hydrodesulfurization catalysts by solvent assisted spreading

Solvent assisted spreading of CoO over monolayer MoO₃/Al₂O₃ catalysts has been studied. CoCO₃ · Co(OH)₂ and CoCO₃ reacted with MoO₃/Al₂O₃ in water slurries. CoO deposition over MoO₃/Al₂O₃ extrudates was followed by EPMA. In the set of eleven MoO₃/Al₂O₃ catalysts, the amount of CoO adsorbed was roughly proportional to the surface area of MoO₃ monolayer. The adsorbed Co species efficiently enhanced the HDS activity.