Mixed Oxide Support Research Articles

Synthesis, characterization and catalytic activity during hydrodesulphurization of dibenzothiophene of NiMoW catalysts supported on Al[sbnd]Ti mixed oxides modified with MgO

Four AlTiMg mixed oxide supports were synthesized by the sol–gel method, adding different MgO loadings (0, 5, 10 and 20wt.%). The samples were characterized by XRD, N2 physisorption, FT-IR spectroscopy, FT-IR pyridine adsorption and UV–Vis DRS. The supports exhibited amorphous mesoporous structures, with average pore size between 3.8 and 7.8nm and high specific surface areas (170–280m2g−1); also, they showed a small presence of carbonates species and weak acid Lewis sites. Synthesized supports were co-impregnated with Ni, Mo and W salts at atomic ratio of Ni/[Ni+(Mo+W)]=0.5. The catalysts were characterized by XRD, N2 physisorption, UV–Vis DRS, Raman spectroscopy and TEM. Catalytic activity and selectivity were evaluated in the hydrodesulphurization (HDS) of dibenzothiophene (DBT) reaction; the results are discussed in terms of the MgO loading to the support. The best catalyst was NiMoW/AlTiMg catalyst with 5wt.% of MgO, which showed better HDS activity than NiMoW/AlTi and a similar performance to that observed for the NiMo/Al2O3 reference catalyst. The activity observed could be correlated to the distribution of active phases on support as well as the pore size distribution. Also, it was found that the direct desulphurization (DDS) pathway was favoured by the trimetallic catalysts; however, the addition of a small loading of MgO (5wt.%) showed a slightly gain towards the hydrogenation pathway (HYD).

Monolayer V2O5/TiO2–ZrO2 catalysts for selective oxidation of o-xylene: preparation and characterization

A series of TiO2–ZrO2 supported V2O5 catalysts with vanadia loadings ranging from 4 to 12 wt% were synthesized by a wet impregnation technique and subjected to various thermal treatments at temperatures ranging from 773 to 1,073 K to understand the dispersion and thermal stability of the catalysts. The prepared catalysts were characterized by X-ray powder diffraction (XRD), BET surface area, oxygen uptake, and X-ray photoelectron spectroscopy (XPS) techniques. XRD results of 773 K calcined samples conferred an amorphous nature of the mixed oxide support and a highly dispersed form of vanadium oxide. Oxygen uptake measurements supported the formation of a monolayer of vanadium oxide over the thermally stable TiO2–ZrO2 support. The O 1s, Ti 2p, Zr 3d, and V 2p core level photoelectron peaks of TiO2–ZrO2 and V2O5/TiO2–ZrO2 catalysts are sensitive to the calcination temperature. No significant changes in the oxidation states of Ti4+ and Zr4+ were noted with increasing thermal treatments. Vanadium oxide stabilized as V4+ at lower temperatures, and the presence of V5+ is observed at 1,073 K. The synthesized catalysts were evaluated for selective oxidation of o-xylene under normal atmospheric pressure in the temperature range of 600–708 K. The TiO2–ZrO2 support exhibits very less conversion of o-xylene, while 12 wt% V2O5 loaded sample exhibited a good conversion and a high product selectivity towards the desired product, phthalic anhydride.

Effect of barium addition on CO oxidation activity of palladium catalysts

CO oxidation over Pd supported on barium fixed alumina (Pd/Ba/Al) and ceria–zirconia mixed oxide (Pd/Ba/CZ) catalysts was investigated by XPS, TPR and in situ DRIFT during light-off using a stoichiometric CO–O 2 mixture. The activity of Pd supported on alumina catalyst was improved by increasing barium loading, but the negative effect was observed for Pd on ceria–zirconia mixed oxide. The role of barium in improving the activity of CO oxidation is considered to weaken the adsorption strength of CO on palladium supported on alumina. On the other hand, barium suppresses the interaction of Pd particles with ceria–zirconia mixed oxide support.

Preparation of a mesoporous ceria–zirconia supported Ni–Fe catalyst for the high temperature water–gas shift reaction

A Ni–Fe/ceria–zirconia catalyst with ordered mesostructure was prepared by the hard-template method employing mesoporous silica (KIT-6) as a template to impart its highly ordered structure to the ceria–zirconia mixed oxide support. Catalytic activities of the Ni–Fe/CeO2–ZrO2 catalyst for the water–gas shift reaction were superior to those of a commercial Fe–Cr-based catalyst. The ordered structure of Ni–Fe/CeO2–ZrO2 catalyst became more stable compared to one prepared without zirconia due to structural stabilization of the mixed oxide by added zirconia in the framework. Alloying of Ni and Fe and enhanced mobility of lattice oxygen in the oxide support may promote its catalytic activity and selectivity for the water–gas shift reaction.

Molecular approaches towards mixed metal oxides and their behaviour in mixed oxide support Au catalysts for CO oxidation

We herein report a water-based sol-gel approach towards porous mixed Si/Ti oxides using co-precipitated glycol-modified precursors. By adjusting synthesis parameters such as the pH value and the Si/Ti ratio of the precursor, the morphology as well as the Si/Ti-composition of the resulting mixed oxide particles can be varied in a wide range. The behaviour of the mixed oxides as substrates for Au catalysts and the performance of the resulting catalysts in the CO oxidation reaction was investigated and compared to catalysts supported on mesoporous anatase and rutile synthesized analogously. For comparable Au particle sizes and Au loadings, the composition of the mixed oxide support was found to significantly affect the reactivity and reaction behaviour, with mixed oxide supported Au catalysts synthesized at pH=5 or 10 and with a Si/Ti-ratio of 1:19 and 1:34 exhibiting the maximum activity. In contrast to the enhanced activity, the mixed oxide supports do not lead to a significant improvement in deactivation behaviour and catalyst stability.

NO Storage-reduction Reaction over Pt–Li<sub>2</sub>O/TiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> Catalysts under SO<sub>2</sub>-containing Conditions

The NO storage-reduction properties of 1 wt% Pt–10 wt% Li2O/TiO2–Al2O3 catalysts prepared by the impregnation and sol-gel methods were investigated in the presence and absence of SO2. The surface area and NO storage amount of catalysts were smaller for the Pt–Li2O/TiO2–Al2O3 catalyst than for the Pt–Li2O/Al2O3 catalyst. However, the Pt–Li2O/TiO2–Al2O3 sample with mixed oxide support achieved high NO removal efficiency for a long period, although the reduction of NO sorption amount by sulfur poisoning was comparable for all catalysts. These results revealed that the mixed oxide support in the catalyst is a key component for continuous NO removal. The preparation method affected the NO storage amount and the crystalline phases of catalysts. The strong diffraction peak of Li2TiO3 phase was observed in the XRD pattern of sample prepared by the impregnation method. The formation of Li2TiO3 weakened the basicity of the catalyst, resulting in decreased NO storage capacity under a SO2-free atmosphere and the enhancement of tolerance to sulfur poisoning.

Characterization of Mn-nanoparticles decorated organo-functionalized SiO2–Al2O3 mixed-oxide as a novel electrochemical sensor: application for the voltammetric determination of captopril

In this work a new sensor in nano size containing Mn–nanoparticles decorated organo-functionalized nanosized SiO2–Al2O3 mixed-oxide support was developed as a new electrocatalysis for oxidation of organic compounds such as captopril. SiO2–Al2O3 mixed–oxide were functionalized with Schiff base ligand and thereatfer, in the next step, Mn–nanoparticles were prepared over the organo–functionalized SiO2–Al2O3 mixed–oxide. The synthesized materials were characterized with different methods such as FT–IR spectroscopy, UV–vis, CHN elemental analysis, TEM, ICP–OES, cyclic voltammetry, and electrochemical impedance spectroscopy. Under the optimum conditions (pH 7.0) in cyclic voltammetry, the oxidation of the captopril was occurred at a potential about 650 mV at a surface of the modified electrode. Linear sweep voltammetry exhibited two wide linear dynamic ranges of 0.30–5.0 and 5.0–340 μmol L−1captopril. The detection limit was found to be 0.095 μmol L−1captopril. The kinetic parameters such as electron transfer coefficient and catalytic reaction rate constant were also determined. Finally, the modified electrode used as a novel electrochemical sensor for the determination of captopril in real samples such as pharmaceutical, patient and safe human urine.

Gold catalysts supported on ceria-modified mesoporous zirconia for low-temperature water–gas shift reaction

New gold catalytic system prepared on ceria-modified mesoporous zirconia used as water–gas shift (WGS) catalyst is reported. Mesoporous zirconia was synthesized using surfactant templating method through a neutral [C13(EO)6-Zr(OC3H7)4] assembly pathway. Ceria modifying additive was deposited on mesoporous zirconia by deposition–precipitation method. Gold-based catalysts with different gold content (1–3 wt. %) were synthesized by deposition–precipitation of gold hydroxide on mixed metal oxide support. The supports and the catalysts were characterized by powder X-ray diffraction, high-resolution transmission electron microscopy, N2 adsorption analysis and temperature programmed reduction. The catalytic behavior of the gold-based catalysts was evaluated in WGS reaction in a wide temperature range (140–300 °C) and at different space velocities and H2O/CO ratios. The influence of gold content and particle size on the catalytic performance was investigated. The WGS activity of the new Au/ceria-modified mesoporous zirconia catalysts was compared with that of gold catalysts supported on simple oxides CeO2 and mesoporous ZrO2, revealing significantly higher catalytic activity of Au/ceria-modified mesoporous zirconia. A high degree of synergistic interaction between ceria and mesoporous zirconia and a positive modification of structural and catalytic properties by ceria have been achieved. It is clearly revealed that the ceria-modified mesoporous zirconia is of much interest as potential support for gold-based catalyst. The Au/ceria-modified mesoporous zirconia catalytic system is found to be effective catalyst for WGS reaction.

Electrochemical and DFT Analysis of Deactivation of Pt Supported on Niobia

The catalytic deactivation of platinum supported on NbRuyOz mixed metal oxide support has been investigated. 60% Pt/NbRuyOz was synthesized in a single step using spray pyrolysis, followed by reductive thermal post-treatment. The catalyst was deposited onto a tabbed, Au TEM grid and rapidly cycled between anodic and cathodic potentials in 0.1M HClO4 and 1M KOH to observe mechanisms of corrosion and deactivation. After 3600 cycles, TEM shows a thin film of oxygen-rich niobia with the potential to block ion transport covering the catalyst and support particles. Density Functional Theory calculations indicate that the rate of oxygen diffusion across the Pt(111) surface is in good agreement with experimental observations of the period of catalyst deactivation (several weeks) when exposed to open atmosphere. This suggests that the mechanism of catalytic deactivation could involve the capture and release of oxygen as Nb2O5 breaks down into reduced fragments of NbOx.

Methane dry reforming with CO 2 on CeZr-oxide supported Ni, NiRh and NiCo catalysts prepared by sol–gel technique: Relationship between activity and coke formation

Ni, NiRh and NiCo catalysts supported on Ce–Zr-oxide synthesised by pseudo sol–gel method have been investigated. Monometallic samples were performed with two different Ce/Zr ratios and by conventional impregnation. BET, XPS, TPR, TPO and TEM were applied for sample characterization and dry reforming of methane was carried out with a feed mixture consisted of CH 4/CO 2/Ar = 10/10/80 or CH 4/CO 2 = 70/30 ratio. Co and Rh containing samples were proved to be stable catalysts, the impregnated Ni catalyst only slightly, while sol–gel Ni samples slowly deactivated during the long term overnight run. The amount of carbon on the sample's surface after catalytic runs varied between 1 and 12 mg C/100 mg of catalyst. The Ni samples prepared by sol–gel and impregnation method had a peak maximum in TPO at 400 °C and 600 °C, respectively. In the case of bimetallic sol–gel samples the carbon that gave TPO peak at 360 °C was slowly transformed to that at 600 °C, showing that after several carbon deposition (dry reforming) and gasification (TPO) cycles structural changes in the catalyst and in the carbon morphology take place and graphitic carbon and nanotube formation become prevailing as was detected by TEM. Upon high temperature pre-treatment and methane dry reforming reaction, alloyed NiRh, NiCo particles and sintered Ni were observed, with the simultaneous presence of carbidic carbon, carbon nanotubes and shell-type graphitic carbon deposition. Support degradation and segregation happened to some extent, but still there was a certain amount of Ni in strong interaction with the support probably still included in the oxide matrix. Broad metal particle size distribution seems to play a role in long term stability. When pure methane was decomposed on Ni catalyst prepared by sol–gel method, the carbonaceous deposit could completely be removed by the subsequent CO 2 treatment, emphasizing the active role of Ce–Zr mixed oxide support in gasification of surface coke.

The generality of surface vanadium oxide phases in mixed oxide catalysts

The nature of VO x sites in mixed oxides of supported VO x (on both pure oxide and mixed oxide supports), molecular sieves, zeolites, clays, hydrotalcites, stochiometric bulk oxides and bulk solid solutions were investigated. For supported metal oxides, zeolites and molecular sieves, the VO x species are exclusively present as surface VO x phases below monolayer coverage or the maximum dispersion limits. For layered clays and hydrotalcites, the VO x is present in the hydroxide layers at modest temperatures and react with the clays and hydrotalcites at higher temperatures (>350 °C) when their layered structures decompose. Surface VO x species are always also present for bulk oxides and bulk solid solutions. The rapid diffusion kinetics of VO x , due to its low Tammann temperature, coupled with the lower surface free-energy of vanadium oxide are responsible for the universal presence of surface VO x sites on all mixed oxide materials. Furthermore, surface reactivity studies demonstrate that the surface VO x sites are the catalytic active sites for all V-containing mixed oxide catalytic materials.

ChemInform Abstract: Comparison of Grafted Vanadia Species on ZrO2, TiO2, SiO2 and TiO2/ SiO2 Mixed Oxides.

Vanadia layers have been deposited onto several zirconia, titania, silica and titania—silica mixed-oxide supports, using the selective reaction of vanadyl triisopropoxide with surface hydroxy groups of the carrier material. The influence of the support, its crystallinity and its crystallographic modification, on the structure of the immobilized vanadia layers were investigated. Surface vanadia species formed upon single and multiple graftings were characterized by Raman, diffuse reflectance FTIR (DRIFT) and UV–VIS diffuse reflectance spectroscopy. On ZrO2, the rapid formation of multilayer structures was observed, as a consequence of the weak interaction between this support and the dispersed vanadia. Comparing the vanadia grafted on low-surface area crystalline ZrO2 with the one grafted on high-surface-area amorphous ZrO2, we noted that the crystallinity and surface area, which are of lesser importance at low coverage, exert an increasing influence on the vanadia structure at higher loadings. On TiO2, small clusters, two-dimensional layer structures and multilayers are identified. The high-surface-area silica support favours a high dispersion of vanadia in the form of clusters and ribbons of limited lateral extent; the influence of the surface hydration state and of thermally induced structural changes of the vanadia species are investigated. On the TiO2/SiO2 mixed-oxide gel, vanadia species are anchored on TiO2 at low loadings and spread out over the SiO2 fractions of the surface at higher coverages.

Catalyst performance of novel Pt/Mg(Ga)(Al)O catalysts for alkane dehydrogenation

The dehydrogenation of ethane and propane using a Pt catalyst supported on a novel Mg(Ga)(Al)O mixed oxide support was investigated. Catalyst performance is strongly dependent on Ga content in the support, a peak in activity for both ethane and propane dehydrogenation occurs at Ga/Pt = 1.4–5.4, and selectivity is a monotonic function of Ga/Pt, reaching nearly 100% at Ga/Pt = 5.4. The addition of hydrogen to the feed resulted in a peak in activity with respect to H 2/alkane. The increase in dehydrogenation rate with H 2 addition is attributed to H-atom-assisted dehydrogenation of alkyl species formed upon dissociative adsorption of the reactant alkane. Beyond the peak in activity with H 2 addition, a further increase in H 2 feed concentration contribute to alkene hydrogenation, thereby reducing the net rate of dehydrogenation. Hydrogen addition to the feed, however, had relatively little effect on alkene selectivity, which remained near 100%. The presence of Ga also suppressed coke formation. Interestingly, less coke was formed during propane dehydrogenation than ethane dehydrogenation, and no correlation was found between coke formation and catalyst deactivation. Thus, the extent of deactivation was lower for ethane than propane dehydrogenation, whereas the amount of coke deposited was higher in the former case. Since the amount of carbon deposited as coke is higher than the amount of exposed Pt, it is concluded that most of the coke resides on the support, and that only a small amount resides on the Pt particles. The higher level of deactivation seen during propane versus ethane dehydrogenation is attributed to a higher coverage of Pt by coke precursors derived from propane than ethane.

Characterization and reactivity of sol–gel synthesized TiO 2–Al 2O 3 supported vanadium oxide catalysts

A 90 wt% TiO 2 in a titania–alumina mixed oxide support (90Ti–Al) was synthesized by the sol–gel method and characterized. Several 90Ti–Al supported vanadium oxide (vanadia) catalysts, xV90Ti–Al, were also synthesized, characterized and probed by the propane oxidative dehydrogenation (ODH) reaction. For the 90Ti–Al support and low vanadia loadings, no rutile peak was observed even after calcination at 1073 K. For vanadia loading greater than 7.5 wt%, rutile peaks were observed at 923 K and higher calcination temperatures. Characterization and reactivity studies suggest that molecularly dispersed, reducible surface vanadia species are present and active for the propane ODH reaction. However, the presence of alumina on the support surface decreased the catalytic activity relative to only titania. The activity variation with calcination temperature had a pronounced effect on the activity of some catalysts and is related to the presence/absence of the surface vanadia species and the surface Al/Ti ratio, both of which change with calcination temperature.

Mixed Oxide Supported MoO3 Catalyst: Preparation, Characterization and Activities in Nitration of o-xylene

TiO2-ZrO2 mixed oxide support was prepared and impregnated with 12 wt % MoO3 and calcined at various temperatures. The resultant catalyst systems were characterized by XRD, FT-IR, BET, SEM, NH3-TPD and pyridine adsorbed FT-IR methods to know the physico-chemical changes occurred in course of thermal treatment. Activities of these catalysts were tested by employing them in the nitration of o-xylene. Mostly, 500 oC calcined catalyst sample was found to be most active for nitration reaction. Catalyst calcined at higher temperatures showed the negative influence on o-xylene conversion and 4-nitro-o-xylene selectivity. Conversion can be correlated with the presence of strong Brönsted acid sites over the catalyst surface whereas change in selectivity was found attributed to the pore diameter of the catalyst. These catalysts also performed satisfactorily, when used for nitration of other aromatics. No use of corrosive sulfuric acid and efficient reusability of the catalyst make the process environmentally friendly and economic. © 2010 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

The Consideration of Splendid Increasing Trend of Green Fuel H<sub>2</sub> Production with the Help of Nanofine Materials

Processes to transform natural gas into hydrogen or synthesis of gas (H2+CO) have been extensively studied in recent decades. H2 can be used in fuel cells as a power source and syngas may be converted into hydrocarbons via the Fischer-Tropsch synthesis. An attractive alternative process for syngas production is the partial oxidation of methane (POM). The objective of this study is to find effective conditions in using of nanofine particles for producing high activity and novel nanocatalysts to syngas, especially selectivity green fuel H2 gas as a power source. Therefore, we could produce 98.6% methane conversion, and 97.1% H2 selectivity with the help of unique stable and new nanofine materials: Eco-friendly x%Ni / SiO2, Co /Ce/ZrO2, Ru / Ce / ZrO2, and highly active Co-Ru and Ni-Ru bimetallic over Ce-ZrO2 nanosized mixed oxide support catalysts. Recently, we prepared new and interesting nanostructures by Cu and Ni sputtering on the nanosized Ce-ZrO2 solid solution support in the first time. Several surfactants, dispersants and mixture of alcohol solvents were applied in synthesis of nanostructures and nanofluids as remarkable templates.

Effect of Ge and CeO 2 on Pt–Ge/Al 2O 3–CeO 2 reforming catalysts

The preparation, characterization and catalytic properties of Pt/Al 2O 3, PtGe/Al 2O 3, Pt/Al 2O 3–CeO and PtGe/Al 2O 3–CeO 2 catalysts are reported. Supports were prepared by impregnating commercial boehmite with cerium nitrate. The solids were calcined at 650 °C to obtain Al 2O 3–CeO 2 mixed oxide supports. The catalysts were characterized by means of H 2 and NH 3 thermodesorption (TPD) measurements, FITR-pyridine and FTIR-CO adsorption spectroscopy. Cyclohexane dehydrogenation and n-heptane reforming reactions were used to evaluate the catalytic activity. It was found that the role of Ge in the bimetallic PtGe catalysts was to dilute the platinum conglomerates, diminishing the number of Pt total surface atoms and inhibiting the Pt hydrogenolytic properties. On the other hand, cerium oxide significantly modified the acidity of the cerium-containing supports. The PtGe/Al 2O 3–CeO 2 catalyst showed a high selectivity towards isomerized olefins in the n-heptane reforming and a high resistance to self-deactivation. It is demonstrated that by inducing modifications to the alumina support, improved catalysts for n-heptane reforming can be obtained.

Copper Promoted Cobalt and Nickel Catalysts Supported on Ceria−Alumina Mixed Oxide: Structural Characterization and CO Oxidation Activity

Catalytic activity of CoO, NiO, CuO−CoO, and CuO−NiO nanocrystalline mono- and bimetallic catalysts over a thermally stable and high surface area ceria−alumina mixed oxide support was evaluated for oxidation of carbon monoxide at normal atmospheric pressure and lower temperatures. The content of Co or Ni in the respective monometallic catalysts was 10 wt % and the Cu-promoted samples contained 5 wt % each. These catalysts were prepared by a wet impregnation procedure and the CeO2−Al2O3 support was obtained by a deposition precipitation method. The synthesized catalysts were characterized by BET surface area, X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDX), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. XRD patterns of 773 K calcined samples revealed the presence of metal oxide phases, namely, CeO2, CuO, NiO, and Co3O4 in the respective catalysts. However, after calcination at 1073 K, the XRD lines ...

Magnetically Separable Gold Catalyst for the Aerobic Oxidation of Amines

AbstractA magnetically separable, recyclable gold catalyst consisting of gold nanoparticles supported on intimately mixed superparamagnetic ceria/iron oxide has been prepared by simple addition of the preformed mixed oxide support and the gold precursor, Au(OAc)3, to the reaction mixture of the aerobic oxidation of amines. The catalyst was characterized by means of X‐ray diffraction (XRD), N2 adsorption, superconducting quantum‐interference device (SQUID) measurements, time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS), scanning transmission electron microscopy (STEM), and scanning electron microscopy with an energy‐dispersive X‐ray spectrometer (SEM‐EDAX). Catalytic tests with various amines showed high selectivity to the corresponding imines (87–100 %), and good separation efficiency and recyclability of the catalyst.

Adsorption and ODH reaction of alkane on sol–gel synthesized TiO 2–WO 3 supported vanadium oxide catalysts: In situ DRIFT and structure–reactivity study

A titania-based mixed-oxide support containing 90 wt% TiO 2, 90Ti–W, and several supported vanadium oxide (vanadia) catalysts, xV90Ti–W ( x = 1–12.5 wt% vanadia), were synthesized and characterized. The anatase phase in the 90Ti–W support remained unaffected up to 1073 K. The presence of vanadia, however, leads to an appearance of the rutile phase and a decrease in the catalyst surface area. The xV90Ti–W catalysts possess surface vanadium and tungsten oxide dispersed species at moderate calcination temperatures. At high vanadia loadings, some interaction between the surface vanadium and tungsten oxide species may exist though bulk supported oxides were not detected. During ethane and propane adsorption, at relatively low adsorption temperatures, acetaldehyde and acetone species were observed, which then oxidized to other adsorbed oxygenated species at higher temperatures. Propane oxidative dehydrogenation (ODH) reaction studies revealed that the propene yield measured at the same conversion increased with increasing loading up to 10 wt% vanadia and then decreased. Analysis of the kinetic parameters showed that the rate constant ratio of propene formation to propene combustion, k 1/ k 2, which represents the propene yield at the same conversion, also increased with vanadia loading. The 10V90Ti–W catalyst was the best amongst this series of catalysts for the propane ODH reaction in terms of activity and propene yield.