Catalytic behaviour and characterisation of CuO1−z(La2O3)z/2 based catalysts deposited on γ-Al2O3 and prepared in situ with 0.0 ⩽z⩽1.00, without and with addition of Pd

(CuO)_1–z(La₂O₃)_z/2 based catalysts with 0.0z1.0 supported on -Al₂O₃ have been prepared in situ and the phases formed have been identified by XRD, SEM and TEM/EDS studies. The catalyst with z=0.5 exhibited the best catalytic activity for oxidation of CO (T ₅₀=295 and 390C with degrees of conversions of 93 and 92% at 450C under rich and lean conditions, respectively) and C₃H₆ (291 and 414C; 93 and 83%) and reduction of NO (405C; 60 and 0%). This catalyst contained appreciable amounts of the perovskite phase LaAl_1–xCu_xO₃ and the enhanced catalytic properties are ascribed to the presence of this phase. Addition of Pd to this catalyst implied that the degree of conversion of NO increased and that the light-off temperatures for all involved gas species decreased. Ageing experiments revealed that LaAl_1–xCu_xO₃ decomposed and that Cu containing Pd particles were formed during this procedure which in turn deteriorated the catalytic properties of the catalyst.     

Epoxidation of Styrene by Anhydrous H2O2 over TS-1 and γ-Al2O3 Catalysts: Effect of Reaction Water, Poisoning of Acid Sites and Presence of Base in the Reaction Mixture

The styrene conversion and product (viz. styrene oxide, phenyl acetaldehyde, benzaldehyde) selectivity in the liquid-phase epoxidation of styrene by H₂O₂ (H₂O₂/styrene = 2) over TS-1 (Si/Ti = 80) and -Al₂O₃ are strongly influenced by the presence of water and/or base (viz. urea and pyridine) in the reaction mixture. The TS-1 showed high styrene conversion activity but no epoxide selectivity in the absence of any base. When anhydrous H₂O₂ (24% H₂O₂ in ethyl acetate), with the continuous removal of the reaction water (using the DeanStark trap), was used instead of 50% aqueous H₂O₂, both the conversion and epoxide yield are increased drastically for the -Al₂O₃, whereas for the TS-1, the increase in the conversion was quite small and there was also no improvement in the epoxide selectivity and/or yield. However, when urea or pyridine was added in the reaction mixture, the epoxide selectivity for both the catalysts was increased depending on the concentration of the base added; the increase in the selectivity was very large for the TS-1 but small for the -Al₂O₃. Poisoning of the acid sites of the -Al₂O₃ by the chemisorbed ammonia or pyridine (at 100 °C) caused a small decrease in the conversion, but it also caused a large decrease in the epoxide selectivity. However, the pyridine poisoning of the TS-1 caused a little beneficial effect, a small increase in the epoxide selectivity. The ammonia poisoning of the TS-1, however, resulted in a small decrease in the conversion with no improvement in the epoxide selectivity. As compared to the TS-1, the -Al₂O₃ catalyst showed a much better performance in the epoxidation by anhydrous H₂O₂ with the continuous removal of the reaction water. However, the reaction water, if not removed continuously, is detrimental to the -Al₂O₃, causing a large decrease in the catalytic activity and selectivity for styrene oxide but an increase in the selectivity for benzaldehyde.     

Microcalorimetric studies of ammonia adsorption on γ-Al2O3, HNa-Y zeolite,and H-mordenite

The acidities of-Al₂O₃, HNa-Y zeolite, and H-mordenite have been examined by microcalorimetric measurements of ammonia adsorption at 423 K. The differential heat of adsorption on -Al₂O₃ decreases continuously with ammonia coverage from an initial value of 165 kJ/ mol at low coverages to a value of 70 kJ/mol at higher coverages. The differential heat of adsorption on HNa-Y zeolite shows similar behavior, with a plateau of nearly constant heat at 115 kJ/mol. H-mordenite exhibits a nearly constant heat of adsorption equal to 155 kJ/mol. The results from these microcalorimetric measurements are in agreement with thermogravimetric and temperature-programmed desorption results collected at higher temperatures. Adsorbed ammonia has sufficient mobility at 423 K to equilibrate with the catalyst surface on the time scale of microcalorimetric measurements, and these measurements provide an effective method for quantifying acid site distributions of solid-acid catalysts.     

The influence of an intermediate MoO3 layer on the solid state reaction of cobalt oxide withγ-Al2O3

In view of the importance for Co_xO_y,-MoO₃/-Al₂O₃ hydrodesulphurization (HDS) catalysts, the reactivity of cobalt oxide layers towards cobalt aluminate formation was investigated on both MoO₃-covered and bare -Al₂O₃ substrates. Co₃O₄/MoO₃/-Al₂O₃ and Co₃O₄/-Al₂O₃ systems were prepared by vapour-deposition of MoO₃ (12 × 10¹⁵ Mo atoms/cm²) and Co (400 × 10¹⁵ Co atoms/cm²) layers onto a -Al₂O₃ substrate, followed by oxidation of the Co layer to Co₃O₄. After annealing at 800°C for 40 h, the interfacial reaction to cobalt aluminate was assessed using Rutherford backscattering spectrometry. The presence of molybdenum oxide appeared to enhance cobalt aluminate formation. The Mo atoms, which spread out over the entire cobalt-containing layer, presumably caused a high defect density, which explains the observed higher reaction rate. The amount of MoO₃ was much too low to stabilize all cobalt atoms by cobalt molybdate formation.     

Low-temperature methanol synthesis catalyzed over Cu/γ-Al2O3–TiO2 for CO2 hydrogenation

A titanium-modified -alumina-supported CuO catalyst has been prepared and used for methanol synthesis from CO₂ hydrogenation. XRD and TPR were used to characterize the phase, reduction property and particle size of the reduced catalyst. The addition of Ti to the CuO/-Al₂O₃ catalyst made the copper in the catalyst exist in much smaller crystallites and exhibit an amorphous-like structure. The adding of Ti made the reduction peak shift toward lower temperature in comparison with the CuO/-Al₂O₃ catalyst. The effect of the addition of Ti and the reaction conditions on the activity and selectivity to methanol from CO₂ hydrogenation were investigated. The activity was found to increase with increasing surface area of metallic copper, but it is not a linear relationship. This indicated that the catalytic activity of the catalysts depends on both the metallic copper area and the synergy between the copper and titanium dioxide. The effect of contact time on the relative selectivity (=SCH₃0H /S_CO) and selectivity of methanol were also investigated. The results indicated that methanol was formed directly from the hydrogenation of CO₂.     

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.     

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.     

Reduction of NO by H2 and CO on PdO-MoO3/γ-Al2O3 of low molybdena loading

The activity and selectivity in the catalytic reduction of NO by a mixture of CO and H₂ of three PdO-MoO₃/-Al₂O₃ catalysts are compared in the presence of varying amounts of oxygen at reaction temperatures from 100 to 550°C. The catalysts were prepared by different methods and contain about 2% Mo and 2% Pd. Results are compared with those for PdO/-Al₂O₃, PdO-MoO₃/-Al₂O₃ containing 2% Pd and 20% Mo, and a commercial Pt-Rh catalyst. The PdO-MoO₃/-Al₂O₃ catalysts are more active for the selective reduction of NO to N₂ and N₂O than PdO/-Al₂O₃ under slightly oxidizing conditions at temperatures from 300 to 550°C. At these reaction conditions, the fresh PdO-MoO₃/-Al₂O₃ catalysts are comparable with a commercial Pt-Rh catalyst. The improved activity of PdO-MoO₃/-Al₂O₃ relative to PdO/-Al₂O₃ is believed to be due to the interaction between Pd and Mo. The effect of O₂ on the activity and selectivity of these catalysts is different in the reduction of NO by H₂, by CO, and by a mixture of H₂ and CO. The results using the mixture of reductants cannot be inferred from the results with the single reductants.     

Reduction of NO by H2 on PdO-MoO3/γ-Al2O3 of low molybdena loading

The catalytic activity and selectivity of three PdO-MoO₃/-Al₂O₃ catalysts containing about 2% Pd and 2% Mo were studied for the reduction of NO by h₂ in the presence of varying amounts of oxygen at temperatures from 50 to 550 °C. The results are compared with those for PdO/-Al₂O₃, PdO-MoO₃/-Al₂O₃ containing 2% Pd and 20% Mo, and a commercial Pt-Rh catalyst. In the absence of oxygen, the conversion of NO to N₂ and N₂O is higher on the three catalysts than it is on PdO/-Al₂O₃ at 500 and 550 °C. In the presence of oxygen, the yields of N₂ and N₂O are generally lower on two of the PdO-MoO₃/-Al₂O₃ catalysts than on PdO/-Al₂O₃.     

Oxidative Conversion of Propane over Al2O3-Supported Molybdenum and Chromium Oxides

Oxidative dehydrogenation of propane has been studied on Mo/-Al₂O₃ catalysts with 13 wt% of MoO₃ and promoted with Cr. The catalysts were characterized by BET, X-ray diffraction, XPS, TPR, TPO and isopropanol decomposition. The ODH results indicated an important increase in propane conversion with Cr loading increase from 0 to 5 wt%. At 773 K the conversion increased 1.5 times whereas the selectivity to propene was not significantly modified. The higher activities obtained on Cr-doped catalysts provide for the technologically important possibility of carrying out the reaction at lower temperatures.     

Reduction of NO by CO on PdO-MoO3/γ-Al2O3 of low molybdena loading

The catalytic activity for the reduction of NO by CO of five PdO-MoO₃/-Al₂O₃ catalysts is compared in the presence of varying amounts of oxygen at reaction temperatures from 25 to 550 °C. The samples were prepared by different methods and contain about 2% of Mo and 2% Pd. Results are compared with the activities and selectivities of PdO/ -A1₂O₃ and PdO-MoO₃/-Al₂O₃ containing 2% Pd and 2% Pd + 20% Mo, respectively. All catalysts showed appreciable activity at temperatures between 300 and 550 °C and at stoichiometric ratios,R, of the oxidizing to reducing gases of 0.1 <R < 1.1. The activity of three PdO-MoO₃/ -A1₂O₃ catalysts with low concentrations of Mo and Pd was found to be significantly higher than the activity of PdO/-Al₂O₃ at 1.1 <R < 1.3 and at temperatures between 300 and 500 °C. The improved activity is ascribed to the interaction of the active metals.     

The Preferential Oxidation of CO: Selective Combinatorial Activity and Infrared Studies

From EXAFS (extended X-ray absorption fine structure) analysis, gold was found to have mainly oxygen in its nearest coordination shell in the fresh Au/-Al₂O₃ catalyst prepared by AuCl₃ impregnation and vacuum drying at room temperature. After thermal treatment under helium, chlorine appeared within the nearest neighbors of gold and more chlorine showed up as the treatment temperature was increased from 323 to 473K. No reduced Au species was observed up to 473K under He. However, the gold became reduced during CO oxidation at 373K and above. The precursor AuCl₃ was found to deposit on -Al₂O₃ via bonding to surface hydroxyl groups. This catalyst showed nearly 100% CO conversion at 573K, but a very low activity at 373 K under the conditions used in this study. Neither the residual chlorine nor the extent of reduction can explain the low activity at lower temperatures.     

Lean NOx catalysis over alumina‐supported catalysts

aluminasupported catalysts show promise as lean NO_x catalysts. The role of alumina in influencing the structural and chemical properties of the active phase supported on it is discussed using some effective aluminabased lean NO_x catalysts. These include Ag/Al₂O₃, CoO_x/Al₂O₃ and SnO₂/Al₂O₃. Alumina plays an important role in stabilizing Ag in the oxidic phase and cobalt in the 2+ oxidation state. For SnO₂/Al₂O₃, alumina increases the SnO₂ surface area. On both Ag/Al₂O₃ and SnO₂/Al₂O₃, alumina also participates actively in the NO_x reduction reaction. An active organic intermediate is formed on Ag or Sn oxide which reacts with NO_x subsequently on alumina to form N₂.     

The effect of steam treatment on MeO/Al2O3 model catalysts (Me = Ni,Co, Cu,Fe)

To study the influence of steam on the solid state reaction between MeO (Me = Ni, Co, Cu or Fe) and Al₂O3, MeO/-Al₂O₃ and MeO/-Al₂O₃ model catalysts were kept in either N₂/20% O₂ or N₂/O₂/30% H₂O at 500–1000°C. The samples were subsequently analyzed with RBS and FTIR. Surprisingly, nickel, cobalt and copper volatilized when MeO/-Al₂O₃ or MeAl₂U₄/-Al₂O₃ samples were annealed in the presence of 0.3 atm steam at 1000°C. Especially copper was found to volatilize very rapidly in the presence of steam, even at a temperature as low as 800°C. FTIR spectra of steam-treated NiO/-Al₂O₃ samples showed the incorporation of hydroxyl groups in the nickel oxide layer. This observation and an excellent agreement with thermochemical calculations support our conclusion that the volatile species are metal hydroxides. The solid state reaction of MeO with-Al₂O₃ was found to proceed at a much higher rate in the presence of 0.3 atm steam at 500–800°C, presumably as a result of an enhanced surface mobility of Me and Al ions along the grain boundaries and the surfaces of the internal pores of the-Al₂O₃ support, when steam is present.     

On the Promotion of Ag/γ-Al2O3 by Cs for the SCR of NO by C3H6

The promotion of Ag/-Al₂O₃ by adding alkali metals (Li, Na, K, Cs) for selective catalytic reduction of NO with C₃H₆ was studied in this work. The activity of NO reduction was enhanced by addition of Cs to Ag/-Al₂O₃ in the presence of excess oxygen and SO₂. The stability and growth of silver oxide particles were promoted and the dispersion of silver particles on -Al₂O₃ was improved by the addition of 0.5 wt% Cs and 1 wt% Cs to 2 wt% Ag/-Al₂O₃, respectively. The results were confirmed by H₂ TPR, UV-Vis DRS, TEM, and XPS.     

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.     

Active-oxygen species on non-reducible rare-earth-oxide-based catalysts in oxidative coupling of methane

From supplementary in situ Raman spectroscopic studies of active-oxygen species on non-reducible rare-earth-oxide-based catalysts in the oxidative coupling of methane (OCM) and structural adaptability considerations, further support has been obtained for our proposal that there may be an active and elusive precursor (of O₂ ^– and O₂ ^2– adspecies), most probably O₃ ^2– formed from reversible redox coupling of an O₂ adspecies at an anionic vacancy with a neighboring O^2– in the surface lattice. This active precursor may initiate H abstraction from CH₄ and be itself converted to OH^–+O₂ ^–, or it may abstract an electron from the oxide lattice and be converted to O₂ ^2–+O^–. The prospect of developing this type of OCM catalysts is discussed.     

31-P NMR study study of acidic sites on Al2O3 and Al2O3-SnO2 after reaction with CCl2F2/H2

The surface acidic properties of two series of samples,-Al₂O₃ and-Al₂O₃-SnO₂ after reaction with CCl₂F₂/H₂ (CFC12/H₂), have been investigated by solid state high resolution CP/MAS 31-PNMR, using trimethylphosphine (TMP) as a probe molecule. It was found after reaction, that Brønsted acid sites were formed on the-Al₂O₃ surface. The longer the reaction time, the more rigidly TMP bonded to the acid sites. For the-Al₂O₃-SnO₂ system, Brønsted acid sites were also found on both the Al₂O₃ and SnO₂ surfaces after reaction of the-Al₂O₃-SnO₂ system with CFC12/H₂. The signal intensity relevant to these sites, indicates that the SnO₂ component is attached to, and therefore covers Brønsted sites of-Al₂O₃. Two types of Lewis acid site initially present on SnO₂ were not observed after reaction with CFC12/H₂.     

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.     

Microcalorimetric and infrared spectroscopic studies ofγ-Al2O3 modified by tin oxides

Microcalorimetric and infrared spectroscopic studies of ammonia and carbon dioxide adsorption have been used to study the effects on the acid/base properties of adding tin oxide to-Al₂O₃. The addition of SnO₂ to-Al₂O₃ decreases the number of strong acid sites (heats of ammonia adsorption higher than 140 kJ/mol), increases the number of weaker acid sites (heats from 110 to 130 kJ/mol), and decreases slightly the number of basic sites (heats of carbon dioxide adsorption from 70 to 150 kJ/mol). In contrast, the presence of SnO on-Al₂O₃ decreases the total number of acid sites (heats of ammonia adsorption higher than 70 kJ/mol) and eliminates most of the basic sites. Infrared spectroscopy of adsorbed ammonia reveals interactions between aluminum cations and stannous ions, leading to a decrease in the strength of the Lewis acid sites associated with aluminum cations.