Investigation of CH4 Reforming with CO2 on Meso-Porous Al2O3-Supported Ni Catalyst

Meso-porous Al₂O₃-supported Ni catalysts exhibited the highest activity, stability and excellent coke-resistance ability for CH₄ reforming with CO₂ among several oxide-supported Ni catalysts (meso-porous Al₂O₃ (Yas1-2, Yas3-8), -Al₂O₃, -Al₂O₃, SiO₂, MgO, La₂O₃, CeO₂ and ZrO₂). The properties of deposited carbons depended on the properties of the supports, and on the meso-porous Al₂O₃-supported Ni catalyst, only the intermediate carbon of the reforming reaction formed. XRD and H₂-TPR analysis found that mainly spinel NiAl₂O₄ formed in meso-porous Al₂O₃ and -Al₂O₃-supported catalysts, while only NiO was detected in -Al₂O₃, SiO₂, CeO₂, La₂O₃ and ZrO₂ supports. The strong interaction between Ni and meso-porous Al₂O₃ improved the dispersion of Ni, retarded its sintering and improved the activated adsorption of CO₂. The coking reaction via CH₄ temperature-programed decomposition indicated that meso-porous Al₂O₃-supported Ni catalysts were less active for carbon formation by CH₄ decomposition than Ni/-Al₂O₃ and Ni/-Al₂O₃.     

Comparison of n-Pentane Reforming Over Pt Supported on Amorphous and γ-Al2O3

The n-pentane reforming activity of Pt supported on nonhydrolytic amorphous Al₂O₃ (Pt/NH–Al₂O₃), was investigated and compared to the catalytic activity of Pt supported on crystalline -Al₂O₃. The Pt was introduced by (a) impregnation with either a solution of H₂PtCl₆ in water or a solution of platinum acetylacetonate (PtAcac) in toluene; (b) in situ introduction of a Pt precursor, either PtBr₄ or cis-bis(benzonitrile)platinum dichloride, before gelation of the NH alumina. The rate-controlling step in the reforming of n-pentane for both amorphous and crystalline aluminas was found to be the reaction on the alumina acidic sites. The Pt/-Al₂O₃ catalysts exhibit higher conversions of n-pentane and higher selectivity to isopentane, than the corresponding amorphous alumina samples. After 1.5 h at 400 °C, the highest conversion of the -Al₂O₃-based catalysts was 47% with 20.3% selectivity to isopentane. The highest conversion of the NH–Al₂O₃-based catalysts under the same conditions was only 26% with 13.6% selectivity to isopentane. The high intrinsic Cl content (2.6wt%) of the amorphous alumina was found to have a minor effect on the activity of the alumina, compared to the activity of the more ordered -alumina. Catalysts prepared by impregnation of the NH alumina with aqueous chloroplatinic acid, exhibited higher conversions compared to catalysts prepared by impregnation of the NH alumina with a solution of PtAcac in toluene. This result occurred in spite of the lower surface area and lower Pt dispersions of the chloroplatinic acid-impregnated catalysts, and is explained by the formation of microcrystalline surface structures and existence of surface chlorine.     

Comparative Study on Partial Oxidation of Methane over Ni/ZrO2, Ni/CeO2 and Ni/Ce–ZrO2 Catalysts

The partial oxidation of methane has been studied by sequential pulse experiments with CH₄ O₂ CH₄ and simultaneous pulse reaction of CH₄/O₂ (2/1) over Ni/CeO₂, Ni/ZrO₂ and Ni/Ce–ZrO₂ catalysts. Over Ni/CeO₂, CH₄ dissociates on Ni and the resultant carbon species quickly migrate to the interface of Ni–CeO₂, and then react with lattice oxygen of CeO₂ to form CO. A synergistic effect between Ni and CeO₂ support contributes to CH₄ conversion. Over Ni/ZrO₂, CH₄ and O₂ are activated on the surface of metallic Ni, and then adsorbed carbon reacts with adsorbed oxygen to produce CO, which is composed of the main path for the partial oxidation of methane. The addition of ceria to zirconia enhances CH₄ dissociation and improves the carbon storage capacity. Moreover, it increases the storage capacity and mobility of oxygen in the catalyst, thus promoting carbon elimination.     

A study of the acidic and catalytic properties of pure and sulfated zirconia–titania and zirconia–silica mixed oxides

Protonated pyridine (PyH⁺) was not found on ZrO₂ (Z) or ZrO₂–TiO₂ (ZT), but was detected on sulfated oxides (ZS, ZTS) by IR spectroscopy. In contrast, ZrO₂–SiO₂ samples containing about 30–80 mol% ZrO₂ showed Brønsted acidity both in nonsulfated (ZS) and sulfated (ZSS) forms. The total acidity was determined by NH₃TPD. Introduction of sulfate ions increased the sitespecific catalytic activity (TOF) in the conversion of cyclopropane or nhexane. The effect of sulfate ions was more significant on samples rich in zirconia. Results suggest that Zr is homogeneously distributed in ZS samples rich in silica. Zirconiabound dimeric sulfate, generating strong acidity, could not be formed in these preparations due to the absence of fairly large ZrO₂ domains.     

Preparation and Characterization of Copper Catalysts Supported on Mesoporous Al2O3 Nanofibers for N2O Reduction to N2

The gas-phase hydrogenation of benzene to cyclohexane over Ce_{1 - x} Pt _x O_{2 -} (x = 0.01, 0.02) catalyst was investigated in the temperature range 80-200 °C. A 42% conversion of benzene to cyclohexane with 100% specificity was observed at 100 °C over Ce_0.98Pt_0.02O_{2 -} with a catalyst residence time of 1.22 × 10⁴ g s/mol of benzene. The activity of the catalyst was compared with those of Pt metal, combustion-synthesized Pt/-Al₂O₃ and Pt/-Al₂O₃. The turnover frequency value of Ce_0.98Pt_0.02O_{2 -} is 0.292, which is an order of magnitude higher than those of the other Pt catalysts investigated. The kinetics of reaction and the deactivation behavior of the catalyst were studied and a regeneration methodology was suggested. The deactivation kinetics and structural evidence from XRD, XPS, TGA and H₂ uptake studies suggest that the oxidized Pt in Ce_0.98Pt_0.02O_{2 -} is responsible for the high catalytic activity towards benzene hydrogenation.     

Catalytic Behavior of Alumina-Promoted Sulfated Zirconia Supported on Mesoporous Silica in Butane Isomerization

Alumina-promoted sulfated zirconia was supported on mesoporous molecular sieves of pure-silica MCM-41 and SBA-15. The catalysts were prepared by direct impregnation of metal sulfate onto the as-synthesized MCM-41 and SBA-15 materials, followed by solid state dispersion and thermal decomposition. Measurements of XRD and nitrogen adsorption isotherms showed that the structures of resultant materials retain well-ordered pores, even with ZrO₂ loading as high as 50 wt%. The characterization results indicated that most of the promoted sulfated zirconia were well dispersed on the internal surface of the ordered mesopores. The catalytic behavior of the alumina-promoted sulfated zirconia supported on mesoporous silica was studied in n-butane isomerization. The supports of mesoporous structures led to high dispersion of sulfated zirconia in the meta-stable tetragonal phase, which was the catalytic active phase. The high performance of alumina-promoted catalysts was ascribed to the sulfur retention by alumina.     

Partial Oxidation Reforming Catalyst for Fuel Cell-Powered Vehicles Applications

Transition metal oxide formulations for the partial oxidation (POX) reforming of isooctane were investigated for an onboard gasoline fuel processor. Ni/M/MgO/Al₂O₃ systems are more active than a commercial ICI catalyst. These catalysts showed better sulfur tolerance over the commercial ICI catalyst in the POX reforming of isooctane containing sulfur (Cs = 100 ppm). There was no apparent deactivation or modification of structure during 770h onstream. It was found that Ni/(Fe,Co)/MgO/Al₂O₃ catalyst is a promising candidate as POX reforming catalyst for gasoline fuel processor applications.     

State of platinum in zirconia and sulfated zirconia catalysts

Platinum is present in a metallic state following activation in air at 725C of both 5 wt% Pt/ZrO₂ and 5 wt% Pt/SO ₄ ^2– /ZrO₂. Reduction of either catalyst at 725C produces a Pt-Zr alloy, and these reduced catalysts, upon recalcination in air at 725C, form metallic Pt crystallites. Likewise, reduction of these uncalcined catalysts at 725C in H₂ leads to a Pt-Zr alloy formation. However, treatment of these uncalcined catalysts in H₂ at 450C does not produce Pt crystallites large enough to detect by XRD.     

Continuous Semihydrogenation of a Propargylic Alcohol over Amorphous Pd81Si19 in Dense Carbon Dioxide: Effect of Modifiers

A novel catalyst, Ni/Ce–ZrO₂, exhibits very high catalytic activity and stability even in the stoichiometric steam reforming of methane (H₂O/CH₄ = 1). Furthermore, when it was employed in oxy-steam reforming, it gave enhanced CH₄ conversion (99.1%) at 750°C and the activity was maintained for 100 h. The high catalyst stability is mainly ascribed to the synergistic effect of the Ce modifier resulting from high capacity to store oxygen and high ability to produce mobile oxygen.     

Steam reforming of n-butane on Pd/ceria

We have examined the steam reforming of n-butane on ceria, 1 wt% Pd/ceria, 1 wt% Pd/alumina, and 15 wt% Ni/silica between 573 and 873 K, with H₂O:C ratios between 1.0 and 2.0. No stable rates could be observed on Ni/silica due to rapid coking under these conditions. While rates were stable on the other catalysts, Pd/ceria showed a much higher activity than either Pd/alumina or ceria individually. Of additional interest, CO₂:CO ratios were much higher on Pd/ceria and approached equilibrium. The reaction order for n-butane on Pd/ceria was 0.15. For H₂O, reaction order changed from 0.6 to zero at the stoichiometric, n-butane:H₂O ratio. It is suggested that the high activity of Pd/ceria for this reaction is due to a dual-function mechanism, in which ceria can be oxidized by H₂O and then supply oxygen to the Pd.     

Catalytic Performance of Pt/ZrO2 and Pt/Ce-ZrO2 Catalysts on CO2 Reforming of CH4 Coupled with Steam Reforming or Under High Pressure

CO₂ reforming of methane was performed on Pt/ZrO₂ and Pt/Ce-ZrO₂ catalysts at 1073K under different reactions conditions: (i) atmospheric pressure and CH₄:CO₂ ratio of 1:1 and 2:1; (ii) in the presence of water and CH₄:CO₂ ratio of 2:1; (iii) under pressure (105 and 190 psig) and CH₄:CO₂ ratio of 2:1. The Pt supported on ceria-promoted ZrO₂ catalyst was more stable than the Pt/ZrO₂ catalyst under all reaction conditions. We ascribe this higher stability to the higher density of oxygen vacancies on the promoted support, which favors the cleaning mechanism of the metal particle. The increase of either the CH₄:CO₂ ratio or total pressure causes a decrease in activity for both catalysts, because under either case the rate of methane decomposition becomes higher than the rate of oxygen transfer. The Pt/Ce-ZrO₂ catalyst was always more stable than the Pt/ZrO₂ catalyst, demonstrating the important role of the support on this reaction.     

Gas phase hydrodechlorination of chlorinated aromatic compounds on nickel catalysts

Supported Ni/-Al₂O₃ catalysts were studied in the gas phase hydrodechlorination of substituted chlorobenzenes. The catalytic properties of the catalysts were shown to be determined by the metal nickel. A correlation between the rate of the gas phase hydrodechlorination of substituted chlorobenzene and donor-acceptor properties of substituents was established. The electron-donor substituents increase and the electron-acceptor ones decrease their reactivity. The correlation analysis of data treated via the Hammett equation shows that hydrodechlorination on Ni/-Al₂O₃ catalysts is a reaction of electrophilic type.     

Support Effect in Supported Ni Catalysts on Their Performance for Methane Partial Oxidation

Supported nickel catalysts were prepared by impregnation of La₂O₃, MgO and ZrO₂ substrates and tested in the partial oxidation of methane to synthesis gas at atmospheric pressure. Nickel interacted strongly with La₂O₃ forming a deficient LaNiO_3- perovskite structure upon calcination. Upon reduction at 973 K, the Ni/La₂O₃ catalysts that resulted were highly active and selective for syngas production. By contrast, a separate and readily reducible NiO phase was formed on the ZrO₂ support. Because the interaction of metallic nickel particles on ZrO₂ is weak, the catalysts underwent deactivation by sintering of metal particles during on-stream operation as confirmed by photoelectron spectroscopy. The relatively high activity of the Ni/MgO systems was associated with the formation of a highly stable cubic Ni-Mg-O solid solution, in which nickel remains highly dispersed during the methane partial oxidation reaction.     

Supported Cu Catalysts with Yttria-Doped Ceria for Steam Reforming of Methanol

The steam reforming of methanol was studied over Cu/Al₂O₃ catalysts with the addition of yttria-doped ceria (YDC). The YDC-modified catalysts were prepared by impregnating a -Al₂O₃ support with Y and Ce then with Cu. The addition of YDC drastically enhanced the activity of Cu/Al₂O₃ in the methanol reforming reaction. The enhanced activity was attributed to the increase of Cu⁺ species by YDC in the methanol reforming environment. However, the addition of YDC decreased the copper dispersion. The Cu dispersion could be enhanced by adding chromium oxide. The addition of YDC and Cr where Al₂O₃ was first impregnated with Cr then with YDC showed the most pronounced enhancement of the catalyst activity. At reaction temperatures of 200250 °C, the CO concentration in the products was smaller than 0.1%.     

Microwave discharge-assisted NO reduction by CH4 over Co/HZSM-5 and Ni/HZSM-5 under O2 excess

Microwave discharge-assisted reduction of NO by CH₄ in the presence of excess O₂ over Co/HZSM-5 and Ni/HZSM-5 catalysts was studied. By comparing the activities of the catalysts in the microwave discharge mode with that in the conventional reaction mode, it is demonstrated that microwave discharge enhanced greatly the conversion of NO to N₂, and expanded the reaction temperature range of the catalysts. For the Co/HZSM-5 catalyst, the conversion of NO to N₂ increased by 30%, and the optimum temperature decreased by 200°C. With the Ni/HZSM-5 catalyst, the highest activity was close to 100%, and the optimum temperature decreased by 325°C. The conversion of CH₄ also increased in the microwave discharge mode over both of the catalysts.     

Synthesis and characterisation of highly dispersed Ni/SiO2 catalysts prepared by gas-phase impregnation/decomposition (GPI/D) of a Ni(II) β-diketonate precursor complex

Silica-supported nickel catalysts have been prepared by a solventless technique involving the deposition of the [Ni(tmen)(acac)₂] precursor from the gas phase. According to UV–vis and IR spectroscopy and to elemental analysis, the initial deposition step results in the grafting of Ni(II) complexes on silanol groups to give predominantly [Ni(acac)₂ (Si-OH)₂]⁰ monomeric inner-sphere complexes, with elimination of the neutral (tmen) ligands into the gas phase. Subsequent thermal treatments in oxidising atmospheres causes an oxidative decomposition of the (acac) ligands without nickel desorption or coalescence into oxide crystallites. The ensuing coordinatively unsaturated Ni(II) centres are reduced to Ni(0) by flowing hydrogen at low temperatures (300 °C), yielding nanosized Ni particles as evidenced by TEM and O₂ titration. Thus, the gas-phase deposition technique represents an interesting alternative to conventional wet deposition procedures since it allows one to obtain well-dispersed supported nickel catalysts by reduction at low-temperatures.     

Comparative studies on direct conversion of methane to methanol/formaldehyde over La–Co–O and ZrO2 supported molybdenum oxide catalysts

The selective oxidation of methane with molecular oxygen over MoO_x/La–Co–O and MoO_x/ZrO₂ catalysts to methanol/formaldehyde has been investigated in a specially designed high-pressure continuous-flow reactor. The properties of the catalysts, such as crystal phase, structure, reducibility, ion oxidation state, surface composition and the specific surface area have been characterized with the use of XRD, LRS, TPR, XPS and BET methods. MoO_x/La–Co–O catalysts showed high selectivity to methanol formation while MoO_x/ZrO₂ revealed the property for the formation of formaldehyde in the selective oxidation of methane. 7 wt MoO_x/La–Co–O catalyst gave 6.7 methanol yield (ca. 60 methanol selectivity) at 420°C and 4.2 MPa. On the other hand, the maximal yield of formaldehyde ca. 4 (47.8 formaldehyde selectivity) was obtained over 12wt MoO_x/ZrO₂ catalyst at 400 °C and 5.0MPa. 7MoO_x/La–Co–O catalyst showed higher modified H₂-consumption than 12MoO_x/ZrO₂ catalyst. The reducibility and the O^–/O^2– ratio of the catalysts may play important roles on the catalytic performance. The proper reducibility and the O^–/O^2– ratio enhanced the production of methanol in selective oxidation of methane. [MoO₄]^2– species in MoO_x/ZrO₂ catalysts enable selective oxidation of methane to formaldehyde.     

High‐activity catalyst of SO 4 2− /ZrO2 supported on γ‐Al2O3 for n‐butane isomerization

A series of Al₂O₃supported SO ₄ ^2– /ZrO₂ superacid catalysts (named SZ/Al₂O₃) were prepared by a precipitation method and their catalytic behavior for nbutane isomerization at low temperature in the absence of H₂ and at high temperature in the presence of H₂ was studied in this paper. The catalytic activities of some of these catalysts were enhanced significantly at both low and high temperatures. At 250°C after 6 h on stream, the steady activity of the most active sample, 60%SZ/Al₂O₃, is about two times higher than that of conventional SZ. The texture properties of catalysts were studied by the methods of XRD and the adsorption of N₂. Experimental evidence of IR of adsorbed pyridine indicates that the significant activity enhancements of SZ/Al₂O₃ catalysts are caused by the increasing of the amount of strong acid sites.     

Selective Production of Hydrogen for Fuel Cells Via Oxidative Steam Reforming of Methanol Over CuZnAl Oxide Catalysts: Effect of Substitution of Zirconium and Cerium on the Catalytic Performance

H₂ fuel, for fuel cells, is traditionally produced from methanol by the endothermic steam reforming of methanol (SRM). Partial oxidation of methanol (POM), which is highly exothermic, has also been suggested as a route to extract H₂ from methanol. In both these reactions a considerable amount of CO is produced as a byproduct, which is a poison to the Pt anode of the fuel cell. A combined steam reforming and partial oxidation of methanol, which has been termed oxidative steam reforming of methanol (OSRM), reported recently is considered to be more efficient and convenient for the selective production of H₂ at a relatively low temperature. The catalysts used in the OSRM reaction were CuZnAl mixed oxides derived from hydroxycarbonate precursors containing hydrotalcite (HT)-like layered double hydroxides (LDHs)/aurichalcite phases. Substitution of Zr for Al in the CuZnAl oxide system was found to improve the catalytic performance. In the present study, the role of added Zr was investigated in detail by employing spectroscopic methods such as X-ray diffraction (XRD), temperature-programmed reduction (TPR), electron paramagnetic resonance (EPR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (AES). The detailed spectroscopic studies revealed that substitution of Zr for Al improved the reducibility and dispersion of copper species due to the operation of a synergistic interaction between copper and zirconium as a consequence of the formation of a Cu²⁺-O-Zr⁴⁺-O- solid solution. The higher catalytic performance of CuZn-based catalysts containing Zr in the OSRM reaction was attributed to the ease of reducibility and enhanced dispersion of copper particles on the support. The substitution of Ce in the CuZnAl system, on the other hand, did not alter the catalytic performance greatly.     

Sol–Gel-Generated La2NiO4 for CH4/CO2 Reforming

A stable La₂NiO₄ catalyst active in CH₄/CO₂ reforming has been prepared by a sol–gel method. The catalyst was characterized by techniques such as XRD, BET, TPR and TG/DTG. The results show that the conversions of CH₄ and CO₂ in CH₄/CO₂ reforming over this catalyst are significantly higher than those over a Ni/La₂O₃ catalyst prepared by wet impregnation and those over a La₂NiO₄/-Al₂O₃ catalyst. The TG/DTG outcome confirmed that the amount of carbon deposition observed in the former case was less than that observed in the latter two cases, a phenomenon attributable to the uniform dispersion of nanoscale Ni particles in the sol–gel-generated La₂NiO₄ catalyst.