Alumina-supported Metal Oxide Research Articles

Catalytic Abatement of VOCs: Aerobic Combustion of Methane or Ethane over Alumina-Supported Metal Oxides Recovered from Spent Catalysts

γ-Al2O3 supported Cu, Cu-Zn and Cu-Ni-Fe-Zn oxide catalysts were prepared using leachate transition metal nitrate and sulfate aqueous solutions from commercial spent catalysts. A bench-scale rig was used to investigate the combustion activity of these catalysts toward methane or ethane in the air stream (1000 ppmv) at a space velocity of 20,000 h-1. The Cu-Ni-Fe-Zn oxides/γ-Al2O3 catalyst proved to be the most active catalyst for the combustion of methane in the temperature range 290-575°C and of ethane in the lower temperature range of 275-525oC as compared to Cu and Cu-Zn oxide loaded catalysts. X-ray powder diffractograms indicated that the metal oxide species were highly dispersed or amorphous on the alumina surface in all the catalysts except for the detection of a minority phase of monoclinic CuO on the Cu-containing mono-metallic catalysts. The co-existence of ZnO in the CuO catalysts suppresses the activity of the copper oxide species and, therefore, the conversion of methane or ethane was reduced. The present research endeavor provides proof-of-concept that relatively inexpensive metal oxide-based heterogeneous catalysts for VOCs abatement can be recovered from spent catalysts. Hence, environmental and health threats of improper handling of VOCs or spent catalysts may be alleviated.

Heterogeneous catalytic ozonation of naphthenic acids in water

AbstractA major challenge the oil sands industries are facing is the urgent need to treat large amounts of oil sands process‐affected water (OSPW). OSPW is toxic to many species mainly due to the presence of naphthenic acids (NAs). Ozonation can significantly reduce both concentration and toxicity of the NAs. Unfortunately, this method suffers from its relatively high cost. To enhance NAs removal, we initiated heterogeneous catalytic ozonation of synthetic OSPW. Two types of catalysts were investigated: i) alumina supported metal oxides, and ii) unsupported catalysts. The alumina supported oxides included MnO2, MnO2/Co3O4, and MnO2/Li2O, while the unsupported catalysts were alumina and activated carbon (AC). All tested catalysts enhanced the ozone removal of NAs. Specifically, AC was found to be a very effective catalyst in addition to its adsorbability. AC significantly enhanced the removal of NAs and COD, the detoxification of the OSPW, and the biodegradability of NAs. For 85 % removal of NAs, the AC catalyzed ozonation needed 15 min whereas over 45 min were required by its non‐catalyzed counterpart. By using AC catalyzed ozonation, the efficiencies of detoxification and COD removal were both over four times and the biodegradability of the synthetic OSPW was over five times of those treated by non‐catalyzed ozonation. The mechanism study confirmed that due to the presence of AC the hydroxyl radical concentration increased 31 %, resulting in 26.4 % reduction in ozone consumption compared to non‐catalyzed ozonation. The removal of NAs was enhanced because of the higher oxidation power of hydroxyl radicals than molecular ozone.

금속 산화물 촉매의 크기와 형태에 따른 질소산화물의 탄화수소 선택적 촉매환원 특성

탄화수소 선택적 촉매환원공정에서 <TEX>${\gamma}$</TEX>-알루미나에 지지된 금속 산화물 촉매의 크기 및 형태에 따른 질소산화물 (<TEX>$NO_x$</TEX>) 저감 특성에 대해 조사하였다. 환원촉매로는 Ag, Cu 및 Ru를 사용하였으며, n-heptane을 환원제로 사용하였다. Ag/<TEX>${\gamma}$</TEX>-<TEX>$Al_2O_3$</TEX> 촉매의 경우 온도범위 <TEX>$250{\sim}400^{\circ}C$</TEX>에서 20 nm>50 nm>80 nm 순으로 Ag의 크기가 작을수록 <TEX>$NO_x$</TEX> 전환효율이 높게 나타났다. 금속 산화물 촉매의 형태에 따른 영향은 구형과 선형에 대해 살펴보았다. Ag와 Cu는 동일한 조건에서 선형이 구형보다 <TEX>$NO_x$</TEX> 전환효율이 높은 것으로 나타났으나, Ru의 경우에는 형태에 따른 영향이 거의 관찰되지 않았다. 사용된 금속산화물 촉매 중에서 Ag를 사용했을 때 <TEX>$NO_x$</TEX> 저감효율이 가장 높았으며, 선형의 Ag를 사용했을 때 <TEX>$300^{\circ}C$</TEX>의 반응온도에서 대부분의 <TEX>$NO_x$</TEX>를 제거할 수 있었다. Cu와 Ru 촉매상에서는 NO가 환원되기보다는 <TEX>$NO_2$</TEX>로의 산화반응이 우세하여 전체적으로 <TEX>$NO_x$</TEX> 저감효율이 낮게 나타났다. This work investigated the size and shape effect of <TEX>${\gamma}$</TEX>-alumina-supported metal oxides on the hydrocarbon selective catalytic reduction of nitrogen oxides. Several metal oxides including Ag, Cu and Ru were used as the catalysts, and n-heptane as the reducing agent. For the Ag/<TEX>${\gamma}$</TEX>-alumina catalyst, the <TEX>$NO_x$</TEX> reduction efficiency in the range of <TEX>$250{\sim}400^{\circ}C$</TEX> increased as the size of Ag decreased (20 nm>50 nm>80 nm). The shape effect of metal oxides on the <TEX>$NO_x$</TEX> reduction was examined with spherical- and wire-shape nanoparticles. Under identical condition, higher catalytic activity for <TEX>$NO_x$</TEX> reduction was observed with Ag and Cu wires than with the spheres, while spherical- and wire-shape Ru exhibited similar <TEX>$NO_x$</TEX> reduction efficiency to each other. Among the metal oxides examined, the best catalytic activity for <TEX>$NO_x$</TEX> reduction was obtained with Ag wire, showing almost complete <TEX>$NO_x$</TEX> removal at a temperature of <TEX>$300^{\circ}C$</TEX>. For Cu and Ru catalysts, considerable amount of NO was oxidized to <TEX>$NO_2$</TEX>, rather than reduced to <TEX>$N_2$</TEX>, leading to lower <TEX>$NO_x$</TEX> reduction efficiency.

Emission Abatement at Small-Scale Biomass Combustion Unit with High-Temperature Catalysts

A newly designed downdraft wood stove achieved low-emission heating by integrating an alumina-supported mixed metal oxide catalyst in the combustion chamber operated under high temperature conditions. In the first step, a catalyst screening has been carried out with a lab-scale plug flow reactor in order to identify the potentially active mixed metal oxide catalysts. Mixed metal oxide catalysts have been the center of attention because of their expected high temperature stability and activity. The catalyst has been synthesized through two novel routes, and it has been integrated into a downdraft wood stove. The alumina-supported mixed metal oxide catalyst reduced the volatile hydrocarbons, carbon monoxide and carbonaceous aerosols by more than 60%.

Facile Synthesis of Ordered Mesoporous Alumina and Alumina-Supported Metal Oxides with Tailored Adsorption and Framework Properties

The evaporation-induced self-assembly (EISA) in ethanolic solution of a triblock copolymer (Pluronic P123) is explored for the synthesis of ordered mesoporous alumina (MA) and MA-supported metal oxides, using aluminum isopropoxide, aluminum chloride, and aluminum nitrate nonahydrate as aluminum precursors, and nickel, magnesium, iron, chromium, copper, cerium, lanthanum, yttrium, calcium, tin chlorides, or nitrates as metal precursors. The as-synthesized mesoporous oxides were characterized by a variety of techniques, such as thermogravimetry, Fourier transform infrared spectroscopy, nitrogen adsorption, small- and wide-angle X-ray diffraction, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry, elemental mapping, and CO2 and NH3 temperature-programmed desorption. It is shown that the EISA strategy in the presence of polymeric template not only is well-suited for the synthesis of ordered MAs and MA-supported metal oxides with tailored adsorption and framework properties, but also ensures a homogeneous distribution of metal species within inorganic framework with the aluminum/metal atomic ratio close to this used in the synthesis mixture. The aluminum and other metal precursors used in EISA have a significant impact on the pore structure, surface area, and basic and acidic properties of the resulting mixed oxides. For instance, the use of inexpensive aluminum nitrate nonahydrate in the synthesis leads to the significantly enlarged mesopores (ranging from ∼7 nm to 16 nm), improved ordering of the oxides, and enhanced adsorption affinity toward CO2, while the aluminum chloride precursor affords MA-supported metal oxides with a bimodal pore size distribution, with peaks located in the ranges of 2−4 nm and 5−9 nm, respectively. It is also shown that the use of inexpensive aluminum and metal salts as precursors instead of aluminum alkoxides affords MA-supported metal oxides with tailorable properties, in terms of the surface area, porosity, and surface basicity and acidity, which determine the performance of these materials in various applications, including adsorption and catalysis.

Ordered Mesoporous Alumina-Supported Metal Oxides

The one-pot synthesis of alumina-supported metal oxides via self-assembly of a metal precursor and aluminum isopropoxide in the presence of triblock copolymer (as a structure directing agent) is described in detail for nickel oxide. The resulting mesoporous mixed metal oxides possess p6 mm hexagonal symmetry, well-developed mesoporosity, relatively high BET surface area, large pore widths, and crystalline pore walls. In comparison to pure alumina, nickel aluminum oxide samples exhibited larger mesopores and improved thermal stability. Also, long-range ordering of the aforementioned samples was observed for nickel molar percentages as high as 20%. The generality of the recipe used for the synthesis of mesoporous nickel aluminum oxide was demonstrated by preparation of other alumina-supported metal oxides such as MgO, CaO, TiO 2, and Cr 2O 3. This method represents an important step toward the facile and reproducible synthesis of ordered mesoporous alumina-supported materials for various applications where large and accessible pores with high loading of catalytically active metal oxides are needed.

Silane Removal at Ambient Temperature by Using Alumina-Supported Metal Oxide Adsorbents

Copper, zinc, and cerium oxide adsorbents supported on alumina were used to remove silane gas (SiH4). The adsorbents were prepared using a coprecipitation method and characterized by the inductively coupled plasma mass spectrometry, X-ray powder diffractometer, and Brunauer-Emmett-Teller method (BET). The si-lane removal efficiency and adsorption capacity of the adsorbents were investigated in this study. Test results showed that the adsorbents containing active species had a removal efficiency >99.9% for SiH4 before breakthrough. Adsorbents containing mixed oxides (CuO-CeO2/ Al2O3 and CuO-ZnO/Al2O3), which showed well-dispersed active species and high BET surface areas, had a greater adsorption capacity than the adsorbents containing single metal oxide. However, when the CuO-ZnO/ Al2O3 adsorbents contain >40 wt% of active metal oxides, the increase of active species lowered the BET surface area leading to a decrease of the adsorption capacity. Additionally, when the content of the active metal oxides was between 20% and 40%, the CuO-ZnO/Al2O3 adsorbents demonstrated higher adsorption capacity.

Effect of Nanosized Gold Particle Addition to Supported Metal Oxide Catalyst in Methanol Oxidation

Gold has rarely been utilized as a catalytic component because of its poor affinity to chemical species. It is however known that nanosized gold particles promote the dissociation of oxygen or hydrogen. In this study, alumina-supported metal oxide catalysts were prepared by impregnation method and applied to methanol oxidation. The dispersion form and size of the gold particles were observed by transmission electron microscopy (TEM). In the results, the maximum catalytic activity was obtained over the ZnO/Al2O3 catalyst, and the optimum loading was 4 wt%. Furthermore, nano-sized gold particles at various loadings were added to ZnO/Al2O3 catalyst by deposition method. The gold particles on Au/ZnO/Al2O3 catalyst were well dispersed and the catalyst activity was remarkably increased compared to ZnO/Al2O3 catalyst. The role of gold particles in the increased catalytic activity is discussed and a possible mechanism is presented.

Effect of Nanosized Gold Particle Addition to Supported Metal Oxide Catalyst in Methanol Oxidation

Gold has rarely been utilized as a catalytic component because of its poor affinity to chemical species. It is however known that nanosized gold particles promote the dissociation of oxygen or hydrogen. In this study, alumina-supported metal oxide catalysts were prepared by impregnation method and applied to methanol oxidation. The dispersion form and size of the gold particles were observed by transmission electron microscopy (TEM). In the results, the maximum catalytic activity was obtained over the ZnO/Al2O3 catalyst, and the optimum loading was 4 wt%. Furthermore, nanosized gold particles at various loadings were added to ZnO/Al2O3 catalyst by deposition method. The gold particles on Au/ZnO/Al2O3 catalyst were well dispersed and the catalyst activity was remarkably increased compared to ZnO/Al2O3 catalyst. The role of gold particles in the increased catalytic activity is discussed and a possible mechanism is presented.

Comparative study on the catalytic activities of alumina-supported metal oxides for oxidation of benzene and cyclohexane with ozone

Catalytic oxidation of benzene and cyclohexane in the gas phase with ozone was carried out at room temperature. The catalytic activities of the oxides of Mn, Fe, Co, Ni, Cu and Ag for the reaction were compared.

Effect of ultra-fine gold particle addition to metal oxides in ethylene oxidation

Oxidation of ethylene was carried out over alumina-supported metal oxide catalysts and highly dispersed gold catalysts, respectively, under atmospheric pressure. The ethylene was completely oxidized to produce carbon dioxide and water with both metal oxide and gold catalysts. The activity of gold catalyst prepared by deposition method was much higher than that of supported metal oxide catalysts. Ultra-fine gold particles on Co3O4 were more active than on Al2O3. Fe2O3/Al2O3 and MnO2/Al2O3 catalysts were more active than MoO3/Al2O3 catalyst. The activity of the supported metal oxide catalysts was greatly enhanced by addition of gold particles. It was therefore considered that gold particles promote dissociative adsorption of oxygen and the adsorbed oxygen reacts with adsorbed ethylene on support adjacent to the active site.

Propane Oxidative Dehydrogenation over Alumina-Supported Metal Oxides

Alumina-supported oxides of V, Cr, Mn, Zr, and Ba were found to catalyze propane oxidative dehydrogenation to propylene at atmospheric pressure, reaction temperatures of 350−450 °C, and a total feed flowrate of 75 cm3/min (26.7% propane, 6.6% oxygen, and the rest helium). Maximum propane conversion (26%) and selectivity to olefin (70%) were achieved with vanadium oxide at 450 °C. The other metal oxides showed lower conversions (9−17%) and olefins selectivities (36−58%). This observation was explained on the basis of the lattice oxygen reactivity as estimated from the reduction potential of the metal cations. Metals whose cations have high potentials (e.g., vanadium oxide catalyst) were found to favor low COx and high selectivity to propene and ethene. This suggests that the metal−oxide bond strength strongly influences the selectivity to olefins in this reaction. A weak linear correlation between the selectivity to propene and the aqueous reduction potential of the cations was found.

Oxidation of Carbon Monoxide Over Alumina-supported Metal Oxide Catalysts

Catalysts of the type CuO/Al2O3, NiO/Al2O3 and Co3O4/Al2O3 with different chemical compositions and subjected to different calcination temperatures were prepared using the impregnation technique. The crystal structure of the calcination products was determined by X-ray diffraction (XRD) while the textural properties were determined from nitrogen adsorption at 77 K. The activity of the catalysts towards the oxidation of carbon monoxide with O2 at different temperatures was also investigated. XRD indicated that calcination of these systems at ≤1073 K did not lead to the formation of spinel. Moreover, no characteristic lines indicating the existence of any metal oxide were observed when the concentration of the latter was less than 10 mol%. The catalytic oxidation of CO followed first-order kinetics with the catalytic activity depending on the metal oxide loading and its dispersion on the surface of the alumina. In most cases, Co3O4/Al2O3 catalysts exhibited the highest activity.

1H MAS NMR Studies of Alumina-Supported Metal Oxide Catalysts

1H MAS NMR Studies of Alumina-Supported Metal Oxide Catalysts

In situ Raman spectroscopy of alumina-supported metal oxide catalysts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIn situ Raman spectroscopy of alumina-supported metal oxide catalystsMichael A. Vuurman and Israel E. WachsCite this: J. Phys. Chem. 1992, 96, 12, 5008–5016Publication Date (Print):June 1, 1992Publication History Published online1 May 2002Published inissue 1 June 1992https://doi.org/10.1021/j100191a051RIGHTS & PERMISSIONSArticle Views4289Altmetric-Citations306LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Acidic properties of alumina-supported metal oxide catalysts: an infrared spectroscopy study

The infrared spectra of the hydroxyl region and that of surface chemisorbed CO 2 species for Re 2 O 7 /Al 2 O 3 , CrO 3 /Al 2 O 3 , MoO 3 /Al 2 O 3 , V 2 O 5 /Al 2 O 3 , TiO 2 /Al 2 O 3 , and Nb 2 O 5 /Al 2 O 3 catalytic systems have been investigated. A sequential consumption of the alumina OH groups upon deposition of the supported metal oxide has been found for all the investigated catalytic systems. A possible relationship between BrOnsted acidity and a new low-frequency band in the hydroxyl region observed at high loadings of the supported metal oxide systems is postulated

Application of Radioactive Tracers in Dehydrocyclization Reaction Mechanisms

Abstract The passage of paraffins and olefins with six or more carbon atoms over catalytic metals and metal oxides can lead to ring closure, Although this reaction was noticed first by three independent groups of Russian workers [1–3], it gained industrial importance through the work of Grosse and co-workers [4] in making toluene from heptane over alumina-supported metal oxide catalysts.

Effect of lead compounds on heterogeneous oxidation catalysts

Studies have been made of the structure, physicochemical characteristic and catalytic activity of a number of unsupported and alumina-supported transition metal oxides as well as of alumina-supported platinum. Measurements have also been made of the effects on these properties of varying amounts of lead bromide and lead chloride, which were introduced onto the surface of the catalysts by means of a fluidised-bed reactor and in all cases caused a reduction in activity.X-ray and thermal studies showed that the observed decrease in catalytic activity could not be attributed to the formation of a new catalytically inactive phase. With unsupported nickel (II) oxide, manganese (IV) oxide and possibly copper (II) oxide, the poisoning effect of the lead halides can, however, be satisfactorily accounted for in terms of the formation of a monolayer of the lead compound on the catalyst surface.The results obtained with unsupported cobalt (II, III, III) oxide are less readily explained. At low temperatures, lead (II) chloride in monolayer amounts caused complete deactivation, but at higher temperatures considerably greater quantities of this compound were needed to eliminate catalytic activity. Under all conditions used, a large excess of lead (II) bromide was required to deactivate this oxide completely. With supported catalysts, the lead halides appeared to be preferentially adsorbed on the alumina support. Again, however, Co3O4/Al2O3 catalysts behaved atypically, in that no such preferential adsorption took place and even sub-monolayer amounts of lead (II) chloride caused complete elimination of catalytic activity.