Catalysts Of Different Compositions Research Articles

Preparation and characterizations of Ni-alumina, Ni-ceria and Ni-alumina/ceria catalysts and their performance in biomass pyrolysis

The catalytic activity of Ni/Al2O3, Ni/CeO2, and Ni/Al2O3-CeO2 catalysts of different compositions were investigated over biomass pyrolysis process. Catalysts were prepared using co-precipitation method with various compositions of nickel and support materials. Surface characterizations of the materials were evaluated using XRD, SEM, and BET surface area analysis with N2 adsorption isotherm. XRD analysis reveals the presence of Al2O3, CeO2, NiO, and NiAl2O4 phases in the catalysts. Paper samples used for daily writing purposes were chosen as biomass source in pyrolysis. TGA experiment was performed on biomass with and without presence of catalysts, which resulted in the decrease of initial degradation temperature of paper biomass with the influence of catalysts. In a fixed-bed reactor, untreated and catalyst mixed biomasses were pyrolyzed up to 800 °C, with a residence time of 15 min. The non-condensable gases were collected through gas bags every after 100 °C and also at 5, 10, and 15 min residence time at 800 °C, which were analyzed using TCD-GC equipment. Comparative distributions of solid, liquid and gaseous components were made. Results indicated diminished amount of tar production in presence of catalysts. 30 wt% Ni/CeO2 catalyst yielded least amount of tar product. The least amount of CO was produced over the same catalyst. According to gas analysis result, 30 wt% Ni doped alumina sample produced maximum amount of H2 production with 43.5 vol% at 800 °C (15 min residence time).

Dependence on composition of electronic properties and stability of Pt–Fe/C catalysts for oxygen reduction

This work presents studies of electronic characteristics and alloy stability carried out for Pt–Fe/C catalysts of different compositions (10–50% Fe, in atoms) and same particle size. The electronic properties are characterized by in situ dispersive X-ray absorption spectroscopy (DXAS). The results show a steady decrease in Pt d-band occupancy as the amount of Fe in the alloy increases. The alloy stability is evaluated by prolonged potential cycling up to 1.0 V. Catalysts with Fe content up to 30% show good stabilities and keep their activities for oxygen reduction after prolonged cycling. In contrast, catalysts with Fe content above 30% suffer pronounced Fe leaching.

Selective reduction of nitrogen oxides by hydrocarbons on hydrotalcite Co and Ni catalysts

Hydrotalcitelike Co-Al and Ni-Al catalysts of different compositions (with the atomic ratio M 2+/Al3+ = 0.5–3.0) were studied in the reaction of selective reduction of NO by propane, propylene, and n-decane in the presence of O2. The higher activity of the catalysts with M 2+/Al3+ = 0.5 is connected with high dispersity of Ni or Co cations stabilized by a significant amount of Al3+ ions. Propylene was shown to be the most efficient reducing agent for nitrogen oxide. The highest degree of conversion to the extent of 90–99% was attained at 400 and 420–440°C for Ni-Al and Co-Al samples, respectively. When propane and decane were used as reducing agents, the conversion of both catalysts was characterized by the volcano-shaped dependence on temperature due to the fact that the catalyst took part in the concurrent reaction of hydrocarbon (reducing agent) oxidation. Hydrotalcitelike materials are promising representatives of inexpensive bi- and multicomponent systems. The design strategy for new active catalysts for processes of purification of gas exhausts from NO x , that are stable in the presence of water and sulfur oxides, may be based on usage of hydrotalcites with modified ions introduced into them.

Synthesis of tetrahydrofuran from maleic anhydride on Cu–ZnO–ZrO2/H-Y bifunctional catalysts

Abstract A series of bifunctional Cu–ZnO–ZrO2/H-Y catalysts of different compositions were prepared by coprecipitating sedimentation method and were characterized by surface area and XRD analyses. The catalytic performance in synthesis of tetrahydrofuran was evaluated and optimized in a three-phase slurry batch reactor. The experimental results showed that the appropriate ratio of Cu/ZnO in the hydrogenation catalyst was 50/45, for which the conversion of maleic anhydride (MA) and selectivity of tetrahydrofuran (THF) reached 100% and 46%, respectively, at 50 bar and 493 K after 6 h of operation. Also, according to these results, it was demonstrated that the incorporation of zirconium oxide in the catalyst formulation enhanced the catalytic activity, and tetrahydrofuran selectivity was increased to 55%. Ultimately, it was concluded that the bifunctional catalyst of Cu–ZnO–ZrO2/H-Y was an appropriate catalyst to produce THF from MA with high activity, selectivity and stability.

Partial oxidation of CH4 to synthesis gas using Ni-catalyst/Au|YSZ|Ag electrochemical membrane reactor

Spc-Ni/MgAl (spc-: solid phase crystallization method) catalyst has been prepared from Mg–Al hydrotalcite-like compounds containing Ni at the Mg site as the precursors and successfully used as a catalyst on an electrochemical membrane reactor for partial oxidation of CH4 at 1173K. The precursors based on [Mg2+A1−xl3+(OH)2x]x+(CO3−)x·mH2O, in which a ratio of Mg/Al varied and a part of Mg2+ ions were replaced by Ni2+ ions, were prepared by co-precipitation method, thermally decomposed, calcined and reduced to spc-Ni/MgAl catalyst. The electrochemical reactor, using yttria-stabilized zirconia (YSZ) as a solid electrolyte, has been employed as an oxygen permeable membrane reactor. The Ni catalyst coupled with Au paste was used as the catalyst-anode, while Ag paste was used as the cathode of the electrochemical cell. The reaction was carried out over the catalyst-anode film under oxygen pumping through the YSZ, and the results were compared with those obtained by various supported Ni catalysts prepared by impregnation (imp-) method. Spc-Ni/MgAl catalysts showed higher activity than imp-Ni catalysts and the best composition of metals in the catalyst was spc-Ni0.5/Mg2.5Al. This catalyst showed the CH4 conversion following the thermodynamic equilibrium between 1023 and 1173K, while the other catalysts of different compositions or imp-Ni catalysts showed a clear decrease in the CH4 conversion with decreasing temperature. Moreover, spc-Ni0.5/Mg2.5Al catalyst showed stable activity during the reaction for 40h. It is concluded that the high and stable activity for the partial oxidation of CH4 is due to highly dispersed and stable Ni metal particles formed on spc-Ni0.5/Mg2.5Al catalyst film.

On the mechanism of fast oxygen storage and release in ceria-zirconia model catalysts

CO oxidation over fresh and aged CexZr1−xO2 (0.15≤x≤1) mixed oxides was carried out under oscillating feed-stream composition by feeding the reactor with CO, He and O2 at a frequency of 0.2Hz. The activity of fresh, high surface area (HSA) catalysts of different compositions is similar and depends mainly on exposed surface redox centers; on the contrary, aged, low surface area (LSA) samples of ceria-zirconia show larger differences of activity with the composition. The sequence and the shape of the product peaks suggest that the kinetics of oxygen storage/release is influenced by surface phenomena that are not taken into account when the reaction is carried out under stationary condition. In particular, in HSA samples the CO2 peak splits into two components. The first component is observed when CO is pulsed over the catalyst, while the second component appears when O2 is pulsed. Temperature and composition of the catalyst determine the intensity ratio of the two peaks. The first peak increases with the amount of zirconia and is the result of direct reaction of CO with the oxygen from the oxide. The second contribution to CO2 production is highly influenced by surface-area and temperature and may be related to a more complex surface dynamic. In situ diffuse reflectance infrared (DRIFT) spectra show that chemisorbed carbonate-like species are involved as intermediates. On the basis of these results, a mechanism and a model for CO oxidation is proposed.

Hydrodechlorination of Tetrachloromethane in the Vapor Phase in the Presence of Pd–Fe/Sibunit Catalysts

The hydrodechlorination of CCl4 in the presence of Pd–Fe/Sibunit catalysts of different composition was studied. An optimum concentration of the metals (2.5% at the ratio Pd/Fe = 1 : 4) was determined, which corresponds to the highest stability of catalysts and selectivity of C2–C4 olefin and paraffin formation. With the use of TPR and magnetic measurements, it was found that the metals occurred in an oxidized state in the course of the reaction; it is likely that this resulted in the formation of C2–C4 hydrocarbons.

Effect of Chemical Composition on the Structure and Catalytic Behaviour of AlPO4 and Al2O3–AlPO4 Mixed Catalysts

AlPO4 and Al2O3–AlPO4 mixed catalysts of different composition (Al/P > 1) were prepared and calcined in the temperature range 350–650°C. Such catalysts were characterized by DTA and X-ray diffraction methods, and by nitrogen adsorption studies at −196°C. Their acidity was determined using a calorimetric titration method while their catalytic activity towards the dehydration of isopropanol was determined using a pulse microcatalytic technique. The data obtained from XRD studies showed that pure AlPO4 when calcined at 650°C had a rather low crystallinity with its crystalline structure (which is of the α-cristobalite type) being characterized by poorly developed peaks. However, significant changes in the texture, surface acidity and catalytic activity were observed as a result of changing the chemical composition of the solid, with the surface area, total pore volume and surface acidity generally increasing with increasing alumina content. Sintering commenced above 550°C leading to a decrease in the surface area and to pore widening. Dehydration of isopropanol appeared to be insensitive to the structure of the catalysts investigated but was related to the surface acid density.

The Dynamics of Oxygen Storage in Ceria–Zirconia Model Catalysts Measured by CO Oxidation under Stationary and Cycling Feedstream Compositions

Measurements were made of the dynamics of CO oxidation over a series of fresh and aged CeO2–ZrO2 catalysts of different composition. In order to evaluate the varying contributions to oxygen storage/release capacity, we carried out the reaction under transient “anaerobic environment” (in both pulse and cycling mode) and steady-state conditions. The presence of ZrO2 was of little or no benefit to stoichiometric CO oxidation carried out under stationary conditions. Under these conditions, catalytic activity is strongly dependent on surface area and on the number of exposed cerium atoms. The highest performance level is achieved with pure ceria. The beneficial effect of CeO2–ZrO2 mixed oxides on catalytic performance was observed when CO oxidation was carried out in transient pulse mode or under cycling feedstream composition. In this case, catalysts having the composition CexZr1−xO2 with 0.5<x<0.8 show an increased catalytic effectiveness correlated to their oxygen storage capacity and redox activity. The promotional effect of ZrO2 was much more evident after severe aging. The decrease in oxygen storage activity with pure CeO2 was higher than that observed for ceria-zirconia and was mainly correlated to the drop in surface area. In contrast with ceria, the low-temperature activity of CeO2–ZrO2 solid solutions for CO oxidation under anaerobic conditions was positively dependent on the degree of reduction of the material. A quantitative estimate of the contribution of bulk diffusion to the overall performance was carried out by calculating the O2− diffusion coefficient. These values were calculated from conductivity measurements using the Nernst–Einstein relation. It is shown that, in the temperature range investigated, bulk diffusion was approximately two orders of magnitude higher for ceri a–zirconia than for ceria and may have been responsible for the enhancement of CO conversion observed with respect to ceria–zirconia-based catalysts.

Crotonaldehyde hydrogenation over alumina- and silica-supported Pt–Sn catalysts of different composition. In situ DRIFT study

Alumina- and silica-supported bimetallic Pt–Sn catalysts with different Pt/Sn atomic ratios have been prepared by using the bimetallic complex cis-[PtCl(SnCl3)(PPh3)2], the monometallic complex cis-[PtCl2(PPh3)2] and SnCl2 as metal precursors. Catalysts have been characterised by X-ray diffraction and transmission electron microscopy techniques, including energy-dispersive X-ray microanalysis, electron diffraction experiments and lattice-fringe microanalysis. The phase composition of the different catalysts has been related to the catalytic behaviour in the vapour phase hydrogenation of crotonaldehyde (but-2-enal). Results show that catalysts containing platinum–tin alloy phases with large particles are more selective towards the hydrogenation of the carbonyl bond to yield crotyl alcohol. The presence of oxidised tin species on the surface of the large alloy particles promotes the hydrogenation of the carbonyl bond. In situ diffuse reflectance infrared spectroscopy studies of crotonaldehyde adsorption under He or H2 reveal differences between bimetallic catalysts and monometallic, and these differences have been related to the different catalytic behaviour of the catalysts.

Structural characterization and catalytic properties of aluminum borates–alumina catalysts

A series of aluminum borate–alumina catalysts of different composition was prepared with the co-precipitation method. The structural and phase changes were studied by thermal analysis, X-ray diffraction (XRD) and FT-IR techniques. Thermal treatment of solid aluminum borates–alumina led to the formation of different phases namely, γ-Al2O3, α-Al2O3, 2Al2O3-B2O3 and 9 Al2O3-2B2O3, where the formation of the latter two phases was observed in the temperature range of 840–900°C. The surface acidities were determined using the spectrophotometric method. Cracking of ethylbenzene and dehydration (DHD) of isopropanol and ethanol were investigated on the calcined catalyst using the pulse microcatalytic technique. The boron contents and the calcination temperature are important factors in determining the structural properties and catalytic activities of these catalysts. The results also indicated that the surface acidities were found to increase with increasing boron contents of the samples and decreased with the calcination temperatures. Therefore, the catalytic activities of the investigated catalysts were found to be structurally sensitive.

Surface Characteristics and Cracking Activity of MoO3–AlPO4 Catalysts

Pure AlPO4 and MoO3–AlPO4 impregnated catalysts of different compositions have been prepared. The catalysts were characterized using XRD and IR techniques. The textural properties were determined from nitrogen adsorption at 77 K. The acidic properties of these catalysts were measured by the amine titration method. The cracking of cumene at flow rates of 20–60 ml/min and at 653–713 K was investigated over these catalysts. Loading AlPO4 with MoO3 leads to a significant change in texture, surface acidity and catalytic activity of the prepared catalysts. The cracking reaction over the investigated catalysts followed first-order kinetics with activation energies of between 8.0 and 20 kcal/mol. The cracking activity has been related to Brönsted acid sites present on the catalyst surface.

Characterization of modified V 2O 5-ZrO 2 catalysts for the oxidative dehydrogenation of propane

V 2O 5-ZrO 2 catalysts of different composition were investigated by means of X-ray diffraction, Laser-RAMAN spectroscopy, temperature programmed reduction and catalytic measurements. At low vanadia contents monomeric vanadyl species and polyvanadate species were found. Alkalimetal additives lead to an increase of the VO bond length in the sequence of nonpromoted < Li < Na < K. The catalytic activity in the oxidative dehydrogenation of propane is connected to the kind of VO x surface species and correlates with the reducibility.

Dehydrogenation of Cyclohexane in Relation to Some Textural and Catalytic Properties of Ni/Al2O3 and Co/Al2O3 Catalysts

Ni/Al2O3 and Co/Al2O3 catalysts of different compositions have been prepared. Their structural properties were determined using X-ray diffraction and differential thermal analysis. The textural properties of these catalysts were determined from nitrogen adsorption at 77 K. The catalysts were reduced with hydrogen at 673 K and the adsorption of hydrogen on the reduced catalysts was measured at 320 K. Dehydrogenation of cyclohexane at flow rates of 10–30 ml/min and at 633–723 K was investigated. The loading of alumina with metal oxides leads to changes in the textural properties depending on the degree of loading and on the loaded metal oxide. The adsorption of hydrogen allowed the determination of important catalytic parameters. Dehydrogenation of cyclohexane on the investigated catalysts followed fraction order kinetics. The dehydrogenation activity has been related to the H2 uptake and to the extent of metal dispersion on the support.

Structural and Surface Properties of CuO-ZnO-Cr2O3 Catalysts and Their Relationship with Selectivity to Higher Alcohol Synthesis

A series of copper-zinc-chromium catalysts of different compositions and calcination temperatures has been prepared, characterized by several techniques (BET specific surface area, XRD, gravimetric TPR, TPD-CO, and XPS), and tested under high alcohol synthesis (HAS) conditions. CO hydrogenation was carried out at reaction temperatures of 523-598 K and 50 bar total pressure. The influence of catalyst composition, calcination temperature, and surface characteristics on the HAS selectivity was studied. The optimum HAS yields were found in the low Cr content region, but chromium was needed. Although chromium oxide does not seem to be involved in the catalytic site, its presence in the catalyst composition is essential, owing to the larger specific surfaces and catalyst stability obtained at the highest reaction temperatures. For low Cr content composition, the temperature-programmed reduction (TPR) profiles were shifted to higher temperatures and simultaneously larger CO2 amounts were found in the temperature-programmed desorption profiles of adsorbed CO (TPD-CO). Photoelectron spectra (XPS) revealed that the oxidation state of copper is Cu2+ in the calcined catalysts and Cu0 in the reduced ones; Cu+ was only stabilized in a CuCr2O4 spinel in the Cr-rich catalysts. These features derived from catalyst characterization are discussed in the framework of the catalytic behaviour for HAS synthesis.

Controlled-environment XRD study of [formula omitted] related to activity in methanol decomposition

Cu ZnO catalysts of different compositions and pretreated under different conditions were studied for methanol decomposition. The structural evolution of the catalyst precursors during pretreatment was monitored by controlled-environment X-ray diffraction (XRD). The catalyst activity is affected by the calcination temperature. High-temperature calcination causes a decrease in the activity. The onset temperature for a significant reduction of the catalyst activity depends on the composition and decreases with increasing Cu composition. XRD studies showed that the catalyst precursors decompose to CuO and ZnO during calcination in air. The onset temperature for the formation of crystalline CuO phase also depends on the composition and decreases with increasing Cu composition. The formation of crystalline CuO species in calcination leads to a metallic Cu phase of low dispersion after subsequent hydrogen reduction. It is believed that Cu is the active species. Thus, the catalyst activity can be related to a phase transition during the pretreatment. The catalyst composition determines the maximum calcination temperature, above which a significant loss in activity in methanol decomposition occurs.

Methanol synthesis from carbon dioxide on CuO-ZnO-A [formula omitted]2O 3 catalysts

Activities and durabilities of CuO-ZnO-A l 2O 3 catalysts for methanol synthesis from H 2, CO 2 and CO were measured in the once-through reaction test using a microreactor. Catalysts of different compositions were prepared by the precipitation method. Activity tests were conducted under the following conditions: temperatures, 210, 230, 250°C; pressures, 40, 80 kgf/cmG; GHSV, 6000 h −1; feed gas composition, H 2/CO 2/CO=77/17/6 (mole%). The result at 250°C, 40kgf/cmG showed that the rates of CO 2 and CO conversion into CH 3 OH were 22–24 % and these values were roughly equal to the equilibrium value (25%). Durability tests at 230°C, 40kgf/cmG found that these catalysts were roughly the same in initial activity for methanol synthesis but considerably different in durability. Additional durability test has been made on the catalyst selected on the basis of the microreactor tests results by recycling unreacted gases, using a bench-scale test plant. The recycling test with this catalyst, conducted for 1000 hours, showed that more than 90% of supplied CO 2 were converted into CH 3 OH under the following conditions: temperature, 240°C; pressure, 80kgf/cmG; make-up gas composition, H 2/CO 2=75/25; GHSV, 5000h −1; recycle ratio, 4 N l /N l .

Partial oxidation of isobutene to methacrolein on BiW/FeCoMoK mixed oxide catalysts

The partial oxidation of isobutene to methacrolein and methacrylic acid was studied on oxidic catalysts containing mainly a mixture of bismuth tungstate and iron cobalt potassium molybdate. The catalysts were prepared via different synthesis methods. The content of bismuth tungstate and iron cobalt potassium molybdate was varied. Catalyst shaping was done by extrusion. The kinetic measurements were performed by monitoring the gas-phase composition along the length of a fixed bed of catalyst. The reactor was treated as an isothermal plug-flow system. The network of parallel and consecutive reactions taking place in this system can be described by a simplified scheme. It is possible to predict the gas-phase composition prevailing in the reactor using five different kinetic parameters. In the temperature range 380°C < ϑ < 420°C grain selectivities as high as 85% combined with yields of methacrolein and methacrylic acid about 70% at 92% conversion were obtained on catalysts prepared via a slurry synthesis method and containing bismuth tungstate in the range between 20 and 70 wt%. Calculations based on the experimentally determined kinetic constants promise an increase in yield if the reactor containing catalysts of different composition is treated at non-uniform temperature. In the case of temperature structuring alone an increase of the methacolein and methacrylic acid yield of about three points has been verified experimentally.

Study on the Internal Action and Existent State of ZrO2 in Fused Iron Catalysts of Different Compositions

By use of XRD, we have found that cubic crystals CaxZr1-x O2-x(CaF2 structure) exist in the fused iron catalyst containing ZrO2 and a small amount of CaO. We also found that Fe2+ could enter monoclinic ZrO2 lattices to convert it into cubic ZrO2(FexZrI-xO2-x), which in turn causes a small portion of Fe3O4 to be broken down to form Fe2O3(10R). SEM observation of the catalyst surface indicates that CaxZrI-xO2-xseparates out of the α-Fe lattice and is concentrated in the cracks or channels of the reduced catalyst, while in the unreduced catalyst, CaxZr1-xO2-x has a relatively uniform dispersion. For the catalyst without CaO, however, ZrO2 exhibits an even distribution on the surface of both reduced and unreduced catalysts. The result of the specific surface area measurement shows that the BET surface area of the catalyst decreases somewhat as the content of ZrO2 increases. By the thermoanalytical technique (TG), we have further confirmed that ZrO2 promotes the reduction of the fused iron catalyst. If ZrO2 and CaO are added together to the catalyst the reduction behavior of the catalyst is greatly improved.

Copolymerization of ethylene with propene in the presence of Ti‐Mg catalysts of different compositions

AbstractComonomer reactivity ratios (from kinetic and 13C NMR data), compositional homogeneity of ethylene‐propene copolymers, and molecular structure of individual fractions of the copolymers obtained with supported Ti‐Mg catalysts of different compositions were determined. The copolymerization reactivity of these systems was found to increase upon introduction of ethyl benzoate and dibutyl phthalate to the catalyst system. It was found that both lowly stereospecific and highly stereospecific catalysts have a broad distribution of active sites with respect to copolymerization reactivity. The composition of the catalysts (titanium content and stereoregulating additives) was shown to influence the reactivity ratios of the comonomers and the microstructure of the copolymers.