Alumina-supported Nickel Catalysts Research Articles

Stable Ni/Al2O3 catalysts for methane dry reforming

To obtain insight into the effect of metal-support interactions in the CO2 reforming of CH4, a series of alumina-supported nickel catalysts were prepared by calcination of the catalyst precursors in air at different temperatures. The increase in the intensity of Ni-Al2O3 interactions with the calcination temperature was found to be unfavorable to the reduction of the catalyst. However, the catalyst with strong Ni-Al2O3 interactions suppressed carbon deposition effectively, which can be attributed to the formation of spinel, NiAl2O4, after calcination. When the reaction was carried out at temperatures higher than 973 K, all the catalysts tended to exhibit equilibrium activity.

Investigation of the Hydrogenation of Some Substituted Alkylbenzenes in a Laboratory Scale Trickle-Bed Reactor

The liquid-phase hydrogenation kinetics of toluene, cumene and mesitylene was studied over an alumina-supported nickel catalyst in a laboratory scale trickle-bed reactor operating isothermally at temperature of 75-115°C and at hydrogen pressures of 20-40 bar. The experiments performed in the absence of intraparticular diffusion resistance showed that the catalyst deactivated rapidly at the initial stage of the experiment, after which a virtually stable level of the catalyst activity was attained. The systematic kinetic experiments carried out with a stable aged catalyst revealed that cumene and mesitylene at high concentrations retarded the hydrogenation rate, whereas such an effect was not observable for toluene. The results of the kinetic experiments were interpreted quantitatively with a reaction mechanism involving sequential addition of hydrogen to absorbed aromatic molecules.

Investigation of the Hydrogenation of Some Substituted Alkylbenzenes in a Laboratory Scale Trickle‐Bed Reactor

The liquid–phase hydrogenation kinetics of toluene, cumene and mesitylene was studied over an alumina-supported nickel catalyst in a laboratory scale trickle-bed reactor operating isothermally at temperature of 75–115°C and at hydrogen pressures of 20–40 bar. The experiments performed in the absence of intraparticular diffusion resistance showed that the catalyst deactivated rapidly at the initial stage of the experiment, after which a virtually stable level of the catalyst activity was attained. The systematic kinetic experiments carried out with a stable aged catalyst revealed that cumene and mesitylene at high concentrations retarded the hydrogenation rate, whereas such an effect was not observable for toluene. The results of the kinetic experiments were interpreted quantitatively with a reaction mechanism involving sequential addition of hydrogen to absorbed aromatic molecules.

CH 4CO 2 reforming anti-carbon deposition catalyst

The reforming of CH 4 with CO 2 was carried out over alumina-supported nickel catalysts with or without La 2O 3 or CeO 2 at 873K and 973K. Rare earth oxides promoted the activity of nickel catalysts 50% and 28% at 873K, 49% and 23% at 973K respectively for La 2O 3 and CeO 2. XRD result showed that rare earth oxides can inhibit the formation of N1AL 2O 4 which is inactive to the reforming of CH 4 and CO 2. XPS result indicated a small increase in the BE of the nickel 2p a a line at oxidation state because of the addition of La 2O 3 or CeO 2. It was observed by TEM that nickel particles entering rate was retarded by La 2O3 and CeO 3.

Conversion of methane and carbon dioxide into synthesis gas over alumina-supported nickel catalysts. Effect of Ni-Al2O3 interactions

A series of alumina-supported nickel catalysts were prepared by calcination of the catalyst precursors in air at different temperatures. The increase in the intensity of Ni-Al2O3 interactions with the calcination temperature was found to be unfavourable to the reduction of the catalyst, and thus caused a decrease in activity for the low temperature reaction between methane and carbon dioxide. However, the catalyst with strong Ni-Al2O3 interactions suppressed carbon deposition effectively, which can be attributed to the formation of spinel, NiAl2O4, after calcination. When the reaction was carried out at 1023 K, all the catalysts tended to exhibit the same activity. At the same time, only filamentous carbon with a hollow inner channel was observed and there were nickel particles on the tip of this filamentous carbon.

Activation of Ni/A12O3 catalysts through modification of the Al2O3 support

The effect of alumina pretreatment on the performance of alumina supported nickel catalysts was demonstrated in gas phase hydrogenation of toluene to methylcyclohexane. The state of the alumina was changed from pure γ to pure θ phase through various heat treatments in air. The catalysts were prepared from vapor phase by saturating the accessible binding sites on the pretreated alumina with the nickel precursor. The highest number of active sites for hydrogenation was observed for catalysts prepared on alumina having an incomplete phase transition and a θ/γ alumina phase ratio between 0.5 and 10. Results from temperature programmed desorption (TPD) studies revealed that a maximum in weakly chemisorbed hydrogen as well as in total amount of desorbed hydrogen was found for the same catalysts. By hydrogen chemisorption studies the total hydrogen uptake was found to correlate with the observed hydrogenation maximum. It is suggested that both the chemical and physical properties of the alumina influence the activity. An optimal metal-support interaction and structural defects on the alumina due to the phase transition can explain the observed maximum in the number of active sites and in hydrogen uptake.

IR evidence for the formation of tilted CO on alumina-supported nickel catalyst

An infrared inactive CO formed on Ni/Al 2O 3 catalyst has been evidenced by the co-adsorption of H 2 at room temperature. The IR inactive CO on Ni/Al 2O 3 could convert into infrared detectable forms, linear and bridged CO, when the catalyst with the pre-adsorbed CO is exposed to H 2, and could also transform into linear and bridged CO as the catalyst is warmed in vacuum. The IR inactive CO might be the tilted CO, whose CO axis is tilted with respect to the nickel surface normal or is nearly parallel to the nickel surface.

Effect of Calcination Temperature on Nickel/Alumina Catalysts

Alumina-supported nickel catalysts prepared by the methods of impregnation and coprecipitation and heated at four different temperatures showed that the optimal calcination temperature for both types of catalysts lies in the region of 623-673 K. Crystallite size measurements by XRD revealed that coprecipitated samples have larger crystallites than the impregnated samples. The total surface areas measured by nitrogen adsorption and the results of metal area measurements made by hydrogen adsorption are in agreement with the crystallite size results.

Influence of organic reagents on alumina supported nickel catalysts. I. Preparation of catalysts

Nickel/γ-alumina catalysts have been prepared by a version of the impregnation technique called double impregnation. The application of different organic reagents for activation of the γ-Al2O3 support promotes the formation of nickel-aluminate and large nickel crystallites in the catalysts obtained.

Effect of alumina supports on the properties of supported nickel catalysts

The objective of this study is to compare the properties and performance of a series of alumina supported nickel catalysts where the only variable is the origin of the alumina. Three commercial aluminas were subjected to a battery of characterization techniques including dissolution studies, X-ray diffraction, nickel adsorption, and measurements of the pH of their point of zero charge. Nickel catalysts formed on these supports were characterized by temperature-programmed reduction, temperature-programmed reaction of carbon monoxide, and temperature-programmed surface reaction. The performance of the catalysts was assessed by CO/H 2 methanation studies. The results from the characterization and performance studies demonstrated that two types of nickel can exist on these alumina supports: a surface nickel and an incorporated nickel. The extent of partitioning between these two states is controlled by the dissolution properties of each alumina when in contact with nickel electrolytes at low pH.

ChemInform Abstract: The H/D Exchange and Hydrogenolysis of Propane on Alumina‐Supported Nickel Catalyst.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The H/D exchange and hydrogenolysis of propane on alumina-supported nickel catalyst

The exchange of propane with deuterium on an alumina-supported nickel catalyst has been studied over a range of temperature (80–190°C) and two hydrocarbon/deuterium ratios. The results are interpreted in terms of a model containing three parameters in which two different adsorbed species are assumed: in the “alkyl” species one H-atom is exchanged in a single adsorption step, and the triadsorbed species exchanges at least three H-atoms per sojourn of the hydrocarbon molecule on the surface of the catalyst. The adsorbed species may undergo multiple exchange per adsorption step. The exchange of CH 3 · CD 2 · CH 3 and CD 3 · CH 2 · CD 3 with H 2 and D 2 was also studied. This showed that the monoadsorbed species is mainly adsorbed at the methyl group and the triadsorbed species twice at a methyl group and once at the methylene group. The hydrogenolysis reactions of propane were studied in the same system between 190 and 240°C. A wide range of conversion was covered, and the product distributions were fitted to kinetic equations in order to obtain the initial rate constants, i.e., selectivities. The nickel/alumina catalyst leads to multiple hydrogenolysis. Several CC bonds are broken before the adsorbed species are desorbed. Under the conditions used in these experiments, surface cracking is the rate-limiting step.

Effect of initial pH value on coke formation of nickel-alumina catalysts in catalytic cracking of n-hexane

Alumina-supported nickel catalysts have been prepared by controlling the initial pH level of Ni(NO 3 ) 2 solution prior to impregnation. The various pH levels used were pH 3, 5, 6, and 8.3. Studies were carried out by performing catalytic cracking of n-hexane in a fixed bed reactor at 733 K and atmospheric pressure. The characterization of prepared catalysts and the carbon content of used ones were analyzed by using X-ray diffraction, temperature-programmed desorption temperature-programmed hydrogenation of the carbon deposit, and chemical analysis for carbon

Effect of thermal treatment on the reducibility of alumina-supported nickel catalysts

The reducibility of a series of alumina-supported nickel catalysts was studied subsequent to various thermal treatments carried out within a temperature-programmed reduction (TPR) apparatus. After thermal treatment at 773 K under argon, the reduced and passivated catalyst showed no reduction profile during TPR. On the other hand, normal reducibility does occur if a TPR procedure is conducted either immediately after room temperature exposure of the reduced catalyst to oxygen or after thermal treatment at 393 K under argon. A model presented earlier [ Appl. Catal., 31 (1988) 229] describing dynamic changes in the structure of alumina-supported nickel catalysts during thermal cycling is consistent with this suppression in reducibility.

Catalytic investigations with the stopped-flow gas chromatographic reactor

The potential of the stopped-flow gas chromatographic reactor (SFGCR) for catalytic investigations was examined through application to methanation studies over alumina-supported nickel and ruthenium catalysts at 375–500 K. It was found that for the SFGCR, the significance of transport resistances could be evaluated more readily than is generally possible with steady state differential flow reactors. Methods for determining the effects of stopped-flow intervals and reversible desorption of reactant on observed rates were also developed. It was demonstrated that for these systems the SFGCR could be operated such that only surface reaction phenomena contributed measurably to observed reaction rates. Rate behavior could be explained by surface heterogeneity, which was substantiated by results from temperature-programmed reaction studies and stopped-flow experiments at varying metal dispersions. The SFGCR was demonstrated to be useful for rapid screening for catalytic activity and structure sensitivity as well as measurement of small rates of reaction.

Dealkylation of coal liquid under CO-steam atmosphere, II. Model reactions using alkylbenzenes on supported nickel catalysts

Dealkylation of alkyl aromatics is a fundamental reaction in the upgrading of coal liquid produced by the usual hydrogenative liquefaction of coal. To develop a catalyst for the studied reaction, we performed the catalytic dealkylation of toluene and of ethylbenzene as model compounds by using a CO/steam mixture under atmospheric pressure at 380–620°C in a conventional flow system with a fixed bed of catalyst. Some runs with H 2 and H 2/steam in place of CO/steam were also perfomed. Both toluene and ethylbenzene are practically inert under CO/steam even at 500°C. Among the various catalysts examined, MgO-supported nickel catalyst was found to be effective for demethylation of toluene. On this catalyst a benzene yield of greater than 30% is obtained from the reaction of toluene at 500°C. The striking feature of the MgO-supported nickel catalyst is the depression of coke formation even at 500°C. The size of the Ni particles in the MgO-supported catalyst is estimated by XRD to be smaller than 10 A. Serious coke formation occurs on silica-supported and alumina-supported nickel catalysts of which activities are usually higher than that of MgO-supported catalyst. The addition of K 2CO 3 to these two catalysts partly depresses coke formation and enhances their catalytic activities. This K 2CO 3 addition effect is primarily due to the fact that potassium increases the dispersion of Ni on the catalyst carrier. The extent of the coke formation is considered to be strongly dependent upon the size of Ni particles. CO/steam mixture is found to be superior to H 2 as a reducing agent, and is especially effective on the MgO-supported nickel catalyst. The supported nickel catalysts facilitate dealkylation of ethylbenzene to give benzene yield of 21.2% and toluene yield of 11.6% at 380°C without serious coke formation.

Kinetic characterization of alumina-supported nickel catalysts for the methanation of carbon monoxide

Methods of kinetic characterization of two different alumina-supported nickel catalysts, which are industrially used for the methanation of carbon monoxide at low concentrations in hydrogen, are discussed: (1) combination of the effective diffusivity of the full-size catalyst pellet with the intrinsic kinetics obtained under conditions which avoided any pore diffusion effects; (2) overall kinetics including pore diffusion as derived from experiments for full-size pellets. By both methods the activity of the catalysts can be predicted in a satisfactory manner. Kinetic measurements were carried out in a gradientless recycle reactor at 448 K ≤ T ≤ 605 K, 0.4 bar ≤ P H2 ≤ 25 bar and 0.0004 bar ≤ P CO ≤ 1.2 bar. Full-size catalyst pellets as well as crushed pellets were used.

Alumina as a nickel catalysts support for steam reforming of hydrocarbons

The coking resistance of six alumina supported nickel catalysts in n-butane steam reforming mainly depends on the average size of nickel crystallites. Thus, by using suitable preparative methods, it is possible to produce good, coking resistant nickel catalysts even with Al2O3 support.

A new method for the determination of particle size distributions from superparamagnetic measurements

The maximum entropy and Backus-Gilbert approaches to data analysis have been adapted and applied to superparamagnetic measurements to obtain particle size distributions together with realistic estimates of their significance. The particle size distributions of three alumina supported nickel catalysts are presented as an illustration.

ChemInform Abstract: KINETICS OF THE METHANATION OF CARBON MONOXIDE ON AN ALUMINA‐SUPPORTED NICKEL CATALYST

Chemischer InformationsdienstVolume 15, Issue 15 Preparative Organic Chemistry ChemInform Abstract: KINETICS OF THE METHANATION OF CARBON MONOXIDE ON AN ALUMINA-SUPPORTED NICKEL CATALYST J. KLOSE, J. KLOSESearch for more papers by this authorM. BAERNS, M. BAERNSSearch for more papers by this author J. KLOSE, J. KLOSESearch for more papers by this authorM. BAERNS, M. BAERNSSearch for more papers by this author First published: April 10, 1984 https://doi.org/10.1002/chin.198415108AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume15, Issue15April 10, 1984 RelatedInformation