Temperature-programmed Reduction Results Research Articles

Catalytic dehydrogenation of cyclohexene over MoO3/γ-Al2O3 catalysts

A series of MoO3/γ-Al2O3 catalysts with different Mo surface densities (Mo atoms/nm2) has been prepared by incipient wetness impregnation method. Structural characteristics of the prepared catalysts were investigated by atomic absorption spectroscopy, X-ray diffraction, Fourier Transform Infrared spectroscopy, N2 adsorption at −196 °C, and temperature-programmed reduction (TPR). The catalytic activities of the prepared catalysts were tested by cyclohexene conversion between 200 and 400 °C. XRD results indicated that molybdenum oxide species were dispersed as a monolayer on the support up to 4.04 Mo atoms/nm2, and the formation of crystalline MoO3 was observed above this loading. FTIR and TPR results showed that molybdenum oxide species were present predominantly in tetrahedral form at lower loading, and polymeric octahedral forms were dominant at higher loading. Cyclohexene conversion reaction proceeded mainly through the simple dehydrogenation pathway in the studied temperature range 200–400 °C and was found to be highly dependent on MoO3 dispersion.

10.2478/s11814-009-0227-2

Two types of CeO2-modified Ni/Al2O3 catalysts were prepared by a consecutive impregnation method with different sequences in the impregnation of Ni and CeO2, and their performance in autothermal reforming (ATR) of isooctane was investigated. Catalysts prepared by adding CeO2 prior to the addition of Ni, Ni/CeO2-Al2O3, produced larger amounts of hydrogen than those obtained using catalysts prepared by adding the two components in an opposite sequence, Ni-CeO2/Al2O3. The results of H2 chemisorption and temperature-programmed reduction revealed that added CeO2 increased the dispersion of the Ni species on Al2O3 and suppressed the formation of NiAl2O4 in the catalyst such that large amounts of Ni species were present as NiO, the active species for the ATR. The elemental and thermogravimetric analyses of deactivated catalysts indicated that Ni/CeO2-Al2O3, which showed a longer lifetime than Ni-CeO2/Al2O3, contained lesser amounts and different types of coke on the surface.

Effects of Pd on enhancement of oxidation activity of LaBO3 (B = Mn, Fe, Co and Ni) pervoskite catalysts for pollution abatement from natural gas fueled vehicles

The effect of Pd on activity enhancement of perovskite catalysts for oxidation of CH4 and CO emitted from natural-gas fueled vehicles is investigated using a synthetic stoichiometric exhaust gas mixture. Various LaBO3 and LaBPd0.05O3 (B=Mn, Fe, Co and Ni) perovskite-type nanocatalysts were prepared via a solution combustion synthesis, calcined at 700°C for 5h, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area measurement, H2 temperature programmed reduction (TPR) and O2 temperature programmed desorption (TPD). XRD results, confirms the presence of PdO in Pd-containing samples, which is highly active for CO and CH4 oxidation. TPR and TPD results show that Pd significantly facilitates the reducibility of B in LaBPd0.05O3 pervoskites and enhances the mobility of lattice oxygen in the prepared samples, which results in activity enhancement for Pd-containing catalysts. Oxidation activity results reveal that Pd effect is more pronounced for CO oxidation as compared to that for CH4, probably due to the Pd transition from PdO to metallic Pd and/or its incorporation into the pervoskite structure occurred at elevated temperatures, which both seem to reduce its activity. Among the prepared samples, LaFePd0.05O3 catalyst shows the highest activity for CO and CH4 oxidation, T90 of which occur at 165 and 558°C, 191 and 40°C lower than that for LaFeO3 respectively.

A simple technique for preparation of presulfided eggshell MoS 2/Al 2O 3 catalysts and kinetics approach for highly selective hydrodesulfurization of FCC gasoline

A new method for the preparation of presulfided eggshell MoS 2/Al 2O 3 catalysts was developed and the catalysts thus prepared were comprehensively characterized and evaluated in terms of their performance in selective hydrodesulfurization (HDS) of FCC gasoline. Using this method, the eggshell thickness of the catalysts with sharp boundary could be easily regulated by controlling the spreading time and/or the temperature of the Mo precursor ([NH 3CH 2CH 2NH 3] 2MoS 4). The characterization by energy-dispersive spectrometry, X-ray diffraction, and high-resolution transmission electron microscopy indicated that the active phase structures, the particle sizes along the basal direction and the stacking degrees of MoS 2 particles on eggshell MoS 2/Al 2O 3 catalysts were similar to these on uniform MoS 2/Al 2O 3 catalysts. Moreover, the results of temperature-programmed reduction and Fourier transformed infrared spectroscopy showed that the method used for the preparation of eggshell catalysts did not affect the nature or number of the MoS 2 active sites compared to these of uniform catalysts. The evaluation of the eggshell catalysts performance, along with corresponding uniform catalysts, in selective HDS of FCC gasoline demonstrated while significant effect of intra-particle diffusion resistance in uniform catalysts was present, the eggshell catalysts remarkably reduced such diffusion effect due to a decreased reactant diffusion path, thus showing higher HDS selectivity.

Chemical Stability and Oxygen Permeability of La0.4Ba0.6Fe1 − xZnxO3 − δ Perovskite: The Effects of Zn Substitution

Perovskite oxide, (LBF), is a typical cobalt-free, mixed ionic–electronic conductor. This work explored B-site doping in LBF by partially substituting iron with Zn, which results in . An investigation on the effects of Zn doping was then conducted. The introduction of Zn in largely augments the concentration of oxygen lattice vacancies and the chemical resistance against reduction in the atmosphere. This conclusion was drawn from the results of X-ray diffraction and temperature-programmed reduction. Furthermore, the temperature-programmed desorption showed us that lattice oxygen desorption is affected by the vacancy concentration and the amount of movable lattice oxygen. The oxygen permeability of the membrane increased from 800 to , with increasing -doping extent (-value) from 0 to 0.1, but the improvement discontinued with further increase in the value from 0.1 to 0.2, namely both ( and 0.2) membranes presented the same oxygen permeation flux as high as at . Nevertheless, perovskite with exhibited superior chemical stability in reducing atmosphere at over that with .

Origination of N2O from NO reduction by NH3 over β-MnO2 and α-Mn2O3

Selective catalytic reduction (SCR) of NO with NH3 was studied on β-MnO2 and α-Mn2O3 catalysts at 150°C and the formation of N2O from SCR was mainly investigated. The activity evaluation showed that the rates of both NO conversion and N2O formation per unit surface area on β-MnO2 were much higher than the corresponding values on α-Mn2O3, while two catalysts gave same generated rate of N2. Transient reactions of NO with NH3 showed that N2O predominantly originated from direct reaction of NO and NH3 via an Eley–Rideal mechanism. β-MnO2 gave higher generated rate of N2O in transient reaction of NH3 and more desorption amount of N2O in temperature-programmed desorption of NH3 than α-Mn2O3. The results of temperature-programmed reduction of H2 exhibited that oxygen species on β-MnO2 are more active than α-Mn2O3. Therefore, β-MnO2 had higher selectivity to N2O in SCR reaction than α-Mn2O3, predominantly resulting from higher activated capability to NH3, and β-MnO2 can cleave more N–H bonds in NH3 molecules to give more adsorbed nitrogen atom species, which reacted with gaseous NO to form more N2O.

CO oxidation over CuO/ZrO2 catalysts: effect of loading and incorporation procedure of CuO

CuO/ZrO2 catalysts were prepared by in situ sol–gel and impregnation methods, with CuO concentrations of 1 and 3·6 mol.-% calcined at 400°C. The catalysts were characterised by SBET, XRD, diffuse reflectance ultraviolet-visible spectroscopy and temperature programmed reduction (H2). The catalytic activity was performed in the CO oxidation. The XRD, diffuse reflectance ultraviolet-visible spectroscopy and temperature programmed reduction results showed that the dispersion of Cu species depends on the method of preparation and on the copper loading. The CuO/ZrO2 catalysts prepared by impregnation procedure showed higher catalytic activity than those prepared by the in situ sol–gel method. This observation can be explained by the presence of small particles of CuO on the catalyst prepared by impregnation (higher dispersion), which does not occur in the catalysts obtained by the in situ sol–gel method due to an important amount of Cu2+ ions that were incorporated into the support network, which are considered catalytically inactive.

Effect of surface properties of activated carbon on CO oxidation over supported Wacker-type catalysts

The effects of chemical pretreatments of the support on CO oxidation over the activated carbon-supported Wacker-type catalyst were studied. Dry oxidation by air at 400 °C and wet oxidation in H 2O 2 and H 3PO 4 aqueous solution were used to modify the physical and chemical properties of activated carbon. The textural and surface characteristics of activated carbons were characterized by nitrogen adsorption, temperature-programmed desorption (TPD) and Boehm titration. The dispersion of active phase and chemical environment of CO oxidation catalysts were investigated by X-ray Photoelectron Spectroscopy (XPS) and temperature-programmed reduction (TPR). CO oxidation results showed that the catalyst prepared using activated carbon with high mesopores and oxygen-functional groups as support performs higher CO oxidation activity at ambient temperature, especially in high relative humidity. XPS and TPR results show that the activated carbon support with enriched oxygen-functional groups would benefit the distribution of active components (Pd 2+, Cu 2+) on the catalyst surface and the formation of easily reducible Cu 2+ species.

Influence of H 2/O 2 redox treatments at different temperatures on Pd-CeO 2 catalyst: Structure and oxygen storage capacity

In order to investigate the metal–support interaction in PM-CeO 2 system, a Pd-doped CeO 2 catalyst was prepared by the sol–gel method and was treated in the H 2–O 2 redox atmosphere at 300, 500 and 800 °C, respectively. The Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results indicate that the redox treatment at 300 °C mainly affect the surface properties of the catalyst, while those at higher temperatures have an influence on the bulk properties. The step-scanning XRD and Raman results prove that Pd species on the surface of the sample mainly exist in the form of bulk Pd and PdO crystallites after the redox treatment at 500 °C, which are encapsulated by CeO 2 particles after the treatment at 800 °C. The CO oxidation activity, dynamic oxygen storage capacity (DOSC) and oxygen storage complete capacity (OSCC) of the catalyst vary with the treating temperature. The 300 °C-treated sample presents the highest activity for CO oxidation and oxygen storage capacity. The reduction-ratio dependent activation energy ( E a) is extremely low for the surface reduction of this sample, suggesting the participation of highly active oxygen. The active oxygen are suggested to originate from the enlarged Pd-Ce interface, which depends on the avaibility of surface Pd sites and contact between metal and support.

High temperature water gas shift catalysts with alumina

Alumina (Al 2O 3) was added as a component of conventional iron oxide-based high temperature water gas shift (WGS) catalysts. The catalysts contained Fe–Al–Cr–Cu–O and were synthesized by coprecipitation. A series of catalysts were prepared with 5–50 wt% Al 2O 3, 8 wt% Cr 2O 3, 4 wt% CuO, and the balance Fe 2O 3. One catalyst was prepared in which the chromia was replaced by alumina. All of the catalysts were compared to a reference WGS catalyst (88 wt% FeO x, 8 wt% Cr 2O 3, and 4 wt% CuO) with no alumina. The catalysts were characterized using temperature programmed reduction (TPR), surface area analysis using nitrogen physisorption, and scanning electron microscopy (SEM) with compositional analysis. The catalysts were also tested kinetically under WGS conditions. Addition of 10–15 wt% alumina increased the catalyst activity and thermal stability, with approximately 15 wt% alumina addition being optimum, as this catalyst produced a reaction rate (normalized per mass) 74% higher than the reference catalyst. The effect of alumina addition was greater than the surface area increase alone, which suggests that alumina alters the activity of the iron oxide domains, likely through an increase in reducibility, as shown by the TPR results. This synergistic effect was only observed when both alumina and chromia were present. Alumina alone (as a replacement for chromia) was not as an effective stabilizer as chromia. Although both the alumina-containing catalyst (without chromia) and the reference with chromia had similar initial surface areas (∼160 m 2/g), the alumina-containing catalyst retained only 74% as much surface area after reaction. Results from the catalysts with 50 wt% alumina suggest that the loss of catalytic activity is also due to the formation of aluminates.

Ethene production by oxidative dehydrogenation of ethane at short contact times over Pt-Sn coated monoliths

The oxidative dehydrogenation of ethane to ethene was studied in a monolithic reactor at short contact times using a Pt-Sn/Al 2O 3 catalyst. The catalyst was characterised by Temperature Programmed Reduction (TPR), Scanning Transmission Electron Microscopy as well as H 2 and CO chemisorption. Three different preparation methods were used for the Pt-Sn catalyst; two-step impregnation where Pt was impregnated first, two-step impregnation where Sn was impregnated first and co-impregnation. The results from the oxidative dehydrogenation of ethane show that the two-step impregnated catalyst with Sn first gave lower ethene selectivity compared to the other impregnation procedures. TPR results indicate that this could be due to a weaker interaction between Pt and Sn in the catalyst. The Pt-Sn catalyst was also compared to LaMnO 3, another catalyst which has been reported to be active for oxidative dehydrogenation of ethane. In these experiments Pt-Sn was found to give superior performance when H 2 was added to the feed. Pt-Sn was clearly more active towards the oxidation of hydrogen compared to LaMnO 3 which was active towards total combustion of hydrocarbons, even when relatively large amounts of hydrogen were present. It seems that ethene is produced mainly in the gas-phase and that the catalyst is important for the oxidation of hydrogen on the surface thus providing heat to the dehydrogenation reactions. However, the results also indicate that there is some ethene production on the Pt-Sn catalyst, either directly or indirectly.

Stability of metal nanoparticles formed during reduction of alumina supported nickel and cobalt catalysts

The formation of nickel and cobalt nanoparticles in hydrogenation catalysts and their stability against sintering during the reduction of the oxidic precursors were investigated. The morphology of the catalysts was manipulated by varying the reduction conditions. The catalysts were characterized using temperature programmed reduction (TPR), hydrogen chemisorption, X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HREM). The transformation of the oxidic precursor into the active phase was monitored using quasi in situ HREM, which proved to be an excellent technique to visualize the formation of metal nanoparticles. For the nickel catalyst the reduction temperature plays a crucial role, whereas time is more critical for the cobalt catalyst. The sintering rate of cobalt is considerably lower than that of nickel during reduction. It is concluded that the activation energy for sintering is significantly higher for nickel than for cobalt. A model is proposed which depicts the structure of both types of catalysts in their oxidic and reduced state. TPR and XPS results indicate that the passivated catalysts contain approximately two oxygen atoms per surface Ni or Co atom.

Selective Catalytic Reduction of NO in Excess Oxygen by Methane over Mn/ZSM-5 Catalysts

The selective catalytic reduction of NO in excess O 2 by CH 4 was investigated over a series of ZSM-5-supported manganese catalysts (Mn/ZSM-5). The catalytic activity depended on preparation method and Mn loading. An ion exchange method resulted in a higher activity than an impregnation method. Catalytic activity increased with increasing Mn loading until a Mn loading of 2.06% that gave a maximum NO conversion of 57.3%. H 2 temperature-programmed reduction results showed that the ion exchange method and low Mn loadings (≤ 2.06%) restricted the formation of non-stoichiometric MnO x (1.5 < x < 2) species that have higher oxidative activity, and thus suppressed the combustion of CH 4 by O 2 , which increased the selectivity for NO reduction. In a SO 2 containing stream, a substantial decrease in NO conversion was seen at ≤ 550 °C but not at ≥ 600 °C. SO 2 temperature-programmed surface reaction and NO temperature-programmed desorption demonstrated that sulfur species were formed at temperature ≤ 550 °C, and these covered active sites and decreased the catalytic activity. The sulfur species desorbed at ≥ 600 °C, thus the addition of SO 2 did not have a significant impact on the catalytic activity. ：考察了富氧条件下 Mn/ZSM-5 催化剂上 CH 4 选择催化还原 NO 反应, 并采用 H 2 程序升温还原、SO 2 程序升温表面反应和 NO程序升温脱附等手段对催化剂进行了表征. 结果表明, 催化剂活性与制备方法和 Mn 负载量密切相关. 离子交换法制备的 Mn/ZSM-5 催化剂活性明显优于浸渍法制备的催化剂; NO 转化率随着 Mn 负载量的增加而增加, 至 2.06% 时达到最大值 (57.3%), 然后随着 Mn 负载量的增加而降低. 采用离子交换法或较低 Mn 负载量 (≤ 2.06%) 抑制了催化剂中非化学计量的 MnO x (1.5 < x < 2) 物种的形成, 减缓了 CH 4 的氧化燃烧反应, 因而 CH 4 还原 NO 的选择性提高. 在含 SO 2 体系中, Mn/ZSM-5 活性在 550 °C 以下时明显下降, 但在 600 °C 以上基本不受影响. 这是由于在 550 °C 以下时 SO 2 在 Mn/ZSM-5 表面形成了稳定的吸附硫物种, 覆盖了部分活性位, 导致催化剂活性降低; 而在 600 °C 以上时含硫物种基本脱附完全, 因而对催化剂活性影响不大. Mn/ZSM-5 prepared by the ion-exchange method with a Mn loading of 2.06% exhibited the maximum NO conversion and was more tolerant to SO 2 poisoning at higher temperature.

Effect of CeO2-addition sequence on the performance of CeO2-modified Ni/Al2O3 catalyst in autothermal reforming of iso-octane

Two types of CeO2-modified Ni/Al2O3 catalysts were prepared by a consecutive impregnation method with different sequences in the impregnation of Ni and CeO2, and their performance in autothermal reforming (ATR) of isooctane was investigated. Catalysts prepared by adding CeO2 prior to the addition of Ni, Ni/CeO2-Al2O3, produced larger amounts of hydrogen than those obtained using catalysts prepared by adding the two components in an opposite sequence, Ni-CeO2/Al2O3. The results of H2 chemisorption and temperature-programmed reduction revealed that added CeO2 increased the dispersion of the Ni species on Al2O3 and suppressed the formation of NiAl2O4 in the catalyst such that large amounts of Ni species were present as NiO, the active species for the ATR. The elemental and thermogravimetric analyses of deactivated catalysts indicated that Ni/CeO2-Al2O3, which showed a longer lifetime than Ni-CeO2/Al2O3, contained lesser amounts and different types of coke on the surface.

Complete oxidation of toluene over bimetallic Pt–Au catalysts supported on ZnO/Al2O3

Bimetallic Pt–Au catalysts supported on ZnO/Al2O3 were prepared by the impregnation (IMP) and incipient wetness impregnation (IW-IMP) methods in air or H2 and compared with a monometallic Pt/ZnO/Al2O3 catalyst. The catalysts were characterized by ultraviolet–visible spectroscopy (UV–vis), X-ray diffraction (XRD), CO chemisorption, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM) in conjunction with energy dispersive spectroscopy (EDS). The catalytic activity for the complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. The relationship between the particle size and catalytic activity for toluene over bimetallic Pt–Au catalysts is discussed. In the results, generally, the Pt particles prepared by IW-IMP in H2 were larger than those prepared by IMP in air. On the other hand, the Au particles prepared by IW-IMP in H2 were smaller than those prepared by IMP in air, namely when using IW-IMP in H2 the Au particle size was decreased and the Pt particle size was increased. Also, the particle sizes of Pt and Au increased with increasing calcination temperature. The STEM and XRD results show that Pt and Au were simultaneously deposited as metallic particles on the ZnO/Al2O3 without forming an alloy with the Pt and Au. From the TPR results, it was found that the nanosized Au particles might promote the reduction of the surface oxygen and that the complete oxidation of toluene shows higher activity at lower temperature over the bimetallic Pt–Au catalysts as compared to the Pt/ZnO/Al2O3 catalyst. The bimetallic Pt–Au catalysts prepared by IW-IMP in H2 calcined at 400°C showed higher activity for complete toluene oxidation.

Ceria modified three-dimensionally ordered macro-porous Pt/TiO 2 catalysts for water-gas shift reaction

Three-dimensionally ordered macro-porous (3DOM) TiO 2 and ceria-modified 3DOM TiO 2 supported platinum catalysts were prepared with template and impregnation methods, and the resultant samples were characterized by scanning electron microscopy(SEM), X-ray diffractometer(XRD), high-resolution transmission electron microscopy(HRTEM) and temperature programmed reduction(TPR) techniques. The catalytic performances over the platinum-based catalysts were investigated for water-gas shift (WGS) reaction in a wide temperature range (180–360 °C). The results showed that 3DOM Pt/TiO 2 catalyst exhibited obviously better catalytic performance than the corresponding non macro-porous catalyst, owing to the macro-porous structure favoring mass transfer. Addition of ceria into 3DOM Pt/TiO 2 led to improvement of catalytic activity. TPR and HRTEM results showed that the interaction existed between ceria and titanium oxide and addition of ceria promoted the reducibility of platinum oxide and TiO 2 on the interface of platinum and TiO 2 particles, which contributed to high activity of the ceria modified catalysts. The results indicated that ceria-modified 3DOM Pt/TiO 2 was a promising candidate of fuel cell oriented WGS catalyst.

Effect of CO pretreatment on the performance of CuO/CeO 2/γ-Al 2O 3 catalysts in CO + O 2 reactions

The influence of CO pretreatment on the properties of CuO/CeO 2/γ-Al 2O 3 catalysts was investigated using X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The activities of the treated catalysts were measured in low-temperature CO oxidation reactions (≤200 °C). For this reaction, the activities of CuO/CeO 2/γ-Al 2O 3 catalysts are intimately related to operation temperature, copper oxide loading amount and CO pretreatment. The influence of the first two factors, i.e., operation temperature and copper oxide loading amount, is similar to the previous results of CuO/γ-Al 2O 3 catalysts [H.Q. Wan, Z. Wang, J. Zhu, X.W. Li, B. Liu, F. Gao, L. Dong, Y. Chen, Appl. Catal. B: Environ. 79 (2008) 254–261]. CO conversions are clearly promoted with increasing operation temperatures and the maximum CO conversions are always reached over the catalysts with a copper oxide loading amount of 0.6 mmol Cu 2+/100 m 2 γ-Al 2O 3, at the set operation temperatures. For the third factor, CO conversions over the CO-treated CuO/CeO 2/γ-Al 2O 3 catalysts are slightly lower than those over the fresh catalysts with the same amount of copper oxide. In contrast, the activity was enhanced over the CO-treated CuO/γ-Al 2O 3 catalysts in the previous report. XRD, TPR and XPS results show that CO pretreatment at 250 °C mainly results in the reduction of crystalline CuO to Cu 0 and of partially dispersed Cu 2+ to Cu + and Cu 0 in CuO/CeO 2/γ-Al 2O 3 catalysts. IR results indicate that besides the CO–Cu + adsorption band at ∼2110 cm −1 on the fresh and CO-pretreated catalysts exposed to CO stream when temperatures are above 50 °C, a new adsorption band at 2170 cm −1 is detectable corresponding to CO–Cu 2+ or CO–Cu 0 over the CO-treated CuO/CeO 2/γ-Al 2O 3 catalysts with copper oxide loading amounts of 0.3 and 1.2 mmol/100 m 2γ-Al 2O 3 at the adsorption temperatures beyond 150 °C. The influences of the ceria modification on the generation of copper species in fresh and CO-treated CuO/CeO 2/γ-Al 2O 3 catalysts and their activities in CO oxidation were discussed.

Study of catalytic decomposition of formaldehyde on Pt/TiO 2 alumite catalyst at ambient temperature

Formaldehyde (HCHO) emitted from buildings, furnishing materials and consumer products is one of the most dominant volatile organic compounds (VOCs) in an indoor environment. In this work, a Pt/TiO 2/Al 2O 3 catalyst was prepared on an anodic alumite plate and was employed in the catalytic decomposition of formaldehyde at ambient temperature. Firstly, TiO 2 was deposited on the anodic alumite plate with electro-deposition technology. Then, platinum was supported on the anodic alumite plate with wet impregnation method. The developed catalyst exhibits good activity towards the decomposition of HCHO at ambient temperature. TPR (temperature programmed reduction) and TPD (temperature programmed desorption) analysis results indicate that oxygen adsorbed on the Pt/TiO 2/Al 2O 3 catalyst can be activated and generated to O:Pt surface species quickly at ambient temperature. Hence, the developed catalyst experiences the high activity towards the catalytic decomposition of formaldehyde at ambient temperature. Moreover, in accordance with the process requirements, the developed catalyst can be formed into various shapes such as a mesh, plate, fin, serrate etc., because aluminum can be formed into any shapes. The serrate type catalyst was prepared in this work and it also exhibits fine activity towards the decomposition of HCHO.

Preparation and characterization of the bimetallic Pt–Au/ZnO/Al 2O 3 catalysts: Influence of Pt–Au molar ratio on the catalytic activity for toluene oxidation

The bimetallic Pt–Au catalysts supported on ZnO/Al 2O 3 with different Pt/Au molar ratios were prepared by impregnation (IMP) method using a mixed solution of Pt and Au precursor. These were characterized by X-ray diffraction (XRD), CO chemisorption, temperature programmed reduction (TPR), and transmission electron microscopy (TEM) equipped energy dispersive spectroscopy (EDS). Catalytic activity for complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. In the results, the aggregation of Au particles depended on the molar ratio in the bimetallic Pt–Au catalyst, and Pt particles was well dispersed homogeneously even by the IMP method. The Pt 75Au 25 and Pt 67Au 33 catalysts concurrently coated with Pt and Au precursors by IMP method showed higher activity than monometallic Pt and Au catalyst for toluene oxidation. Also, in order of the catalytic activity for toluene was very good agreement compare with the TPR results. The Au particles might promote the toluene oxidation over the bimetallic catalyst concurrently coated with Pt and Au particles. Therefore, the size of Pt and Au particles and catalytic activity were confirmed to be correlated to molar ratio of Pt and Au loaded.

Mesoporous silica–alumina as support for Pt and Pt–Mo sulfide catalysts: Effect of Pt loading on activity and selectivity in HDS and HDN of model compounds

The potential of mesoporous silica–alumina (MSA) material as support for the preparation of sulfided Pt and Pt–Mo catalysts of varying Pt loadings was studied. The catalysts were characterized by their texture, hydrogen adsorption, transmission electron microscopy, temperature programmed reduction (TPR) and by activity in simultaneous hydrodesulfurization (HDS) of thiophene and hydrodenitrogenation (HDN) of pyridine. Sulfided Pt/MSA catalysts with 1.3 and 2wt.% Pt showed almost the same HDS and higher HDN activities per weight amounts as conventional CoMo and NiMo/Al2O3, respectively. The addition of Pt to sulfided Mo/MSA led to promotion in HDS and HDN with an optimal promoter content close to 0.5wt.%. The results of TPR showed strong positive effect of Pt on reducibility of the MoS2 phase which obviously reflects in higher activity of the promoted catalysts. The activity of the MSA-supported Pt–Mo catalyst containing 0.5wt.% Pt was significantly higher than the activity of alumina-supported Pt–Mo catalyst. Generally, Pt–Mo/MSA catalysts promoted by 0.3–2.3wt.% Pt showed lower HDS and much higher HDN activities as compared to weight amounts of CoMo and NiMo/Al2O3. It is proposed that thiophene HDS and pyridine hydrogenation proceed over Pt/MSA and the majority of Pt–Mo/MSA catalysts on the same type of catalytic sites, which are associated with sulfided Pt and MoS2 phases. On the contrary, piperidine hydrogenolysis takes place on different sites, most likely on metallic Pt fraction or sites created by abstraction of sulfur from MoS2 in the presence of Pt.