Catalysts For Partial Oxidation Of Methane Research Articles

The Effect of Nb Loading on Catalytic Properties of Ni/Ce 0.75Zr 0.25O 2 Catalyst for Methane Partial Oxidation

In this study, the effect of Nb loading on the catalytic activity of Ce 0.75Zr 0.25O 2-supported Ni catalysts was studied for methane partial oxidation. The catalysts were characterized by BET, H 2 chemisorption, XRD, TPR, TEM and tested for methane partial oxidation to syngas in the temperature range of 400–800 °C at atmospheric pressure. The results showed that the activity of methane partial oxidation on the catalysts was apparently dependent on Nb loading. It seemed that the addition of Nb lowered the catalytic activity for methane partial oxidation and increased the extent of carbon deposition. This might be due to the strong interaction between NiO and Nb-modified support and reduction of surface oxygen reducibility.

Influence of Supports on Catalytic Performance and Carbon Deposition of Palladium Catalyst for Methane Partial Oxidation

The catalytic performance of methane partial oxidation was investigated on Pd/CeO 2-ZrO 2 and Pd/α-Al 2O 3 catalysts. The catalysts were characterized by XRD, Raman spectra, and TG-DTA techniques. The results show that CeO 2-ZrO 2 support is more advantageous for the catalytic activity and stability of catalysts compared to α-Al 2O 3. TG-DTA and Raman spectra results indicated that carbon deposited on the catalysts was in the form of graphite, which is the main reason for the deactivation of catalysts after a 24-hour reaction. Moreover, CeO 2-ZrO 2 had positive effect on inhibiting carbon deposition.

Effect of Ce/Zr ratio on the performance of Pt/CeZrO 2/Al 2O 3 catalysts for methane partial oxidation

In this work the effect of Ce/Zr ratio on Pt/Ce x Zr 1− x O 2/Al 2O 3 catalysts prepared by impregnation was studied. The samples were tested for the partial oxidation of methane and characterized by different techniques such as temperature-programmed reduction, oxygen storage capacity, and infrared spectroscopy of adsorbed CO 2. The platinum dispersion was determined through the cyclohexane dehydrogenation and the results showed that the metallic dispersion was approximately the same for all samples. However, among all the catalysts tested the sample Pt/CeO 2/Al 2O 3 and Pt/Ce 0.50Zr 0.50O 2/Al 2O 3 presented the higher activity and stability for the methane partial oxidation reaction. This result could be due to a good distribution of the ceria-based oxide on the alumina surface, a good reducibility and a high oxygen storage capacity verified for these samples. All these characteristics contributed to the removal of coke formed on the active sites formed during the reaction, avoiding the sample's deactivation.

Effects of catalyst heating rates upon the activity of silica-supported silicomolybdic acid catalysts for methane partial oxidation

Silica-supported silicomolybdic acid (SMA) catalysts showed a very high activity for partial oxidation of methane into formaldehyde at 873 K in the presence of an excess amount of water vapor in feed. However, the high activity was observed only when the catalysts were heated to 873 K with very high heating rates such as 100 K min-1. In this article, the reason why these high heating rates are necessary to exhibit the higher catalytic activity into formaldehyde will be discussed based on the structural changes in SMA during heating the catalysts to 873 K.

Effect of mixed rare-earth additive on Ni/Al 2O 3 catalyst for methane partial oxidation to syngas

Effect of mixed rare-earth additive on Ni/Al 2O 3 catalyst for methane partial oxidation to syngas

Zirconia-based SOFC with non-noble electrodes fed by air–methane mixture

One- and two-chamber solid oxide fuel cells (SOFCs) fed by an air–methane mixture (AMM) were studied at 550–700°C. (Y 2O 3) 0.04(Sc 2O 3) 0.06(ZrO 2) 0.9 was used as a solid electrolyte, ceria-doped Ni-YSZ-cermet (CNC) and SrO-doped LaMnO 3 (LSM) were used as electrodes. In the experiments with the two-chamber cell, it was stated that the LSM-electrode did not catalyse methane partial oxidation and its potential was close to the potential of free oxygen mixed with methane and nitrogen. The CNC-electrode was a good catalyst for methane partial oxidation and its potential was close to the potential of the mixture formed in methane partial oxidation process. In the one-chamber cell, the current density was about 15 mA/cm 2 at the terminal voltage 500 mV within an interval of 550–650°C.

Toward new Pt- and Rh-based catalysts for methane partial oxidation at high temperatures and short contact times

Abstract At high temperatures, using conventional supports (SiO2, Al2O3) usually an important deactivation is observed due to particle sintering. In this study, we have prepared 1.0 wt. % Pt and Rh 0.5 wt. % catalysts supported on a new Si3N4 ceramic by using impregnation with Pt(C5H7O2)2 and Rh(NO3)2. The catalytic performances were evaluated between 900 and 1 100 °C at contact times between 0.35 and 6.90 ms at atmospheric pressure. The feed was a CH4/O2/N2≈2/1/10 mixture. These materials were found to present an exceptional thermal stability with a minor particle sintering. Metal loss was observed only for the platinum catalyst. © 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS

Designing oxidation catalysts

A simplified approach is described for the design of oxidation catalysts. It is based on three components and for selective oxidation the approach involves identifying catalysts that (a) do not catalyse the oxidation of the required product under the reaction conditions to be tested, (b) activate the oxidant and (c) activate the substrate. This approach is initially demonstrated to identify components of novel methane oxidation catalysts for the formation of methanol. The approach seeks to identify oxides that are capable of activating methane and oxygen, but do not destroy methanol, the desired product. From the perspective of methanol stability the oxides MoO 3, Nb 2O 5, Ta 2O 5 and WO 3 all produced high methanol conversion, however, high selectivities towards formaldehyde and dimethylether were obtained, with only low levels of carbon oxides throughout the range of conversions. The products formaldehyde and dimethylether were desirable by-products from a methane partial oxidation process, hence these oxides are considered to be suitable catalyst components. The activation of oxygen was probed using the 16 O 2/ 18 O 2 exchange reaction. The activation of methane has been probed by the exchange reaction with deuterium under non-oxidative conditions. The most active catalyst was Ga 2O 3 which exhibited normalised exchange rates several orders of magnitude greater than the other catalysts. On the basis of these results we tested a simple two component oxide catalyst for methane partial oxidation based on a Ga 2O 3/MoO 3 physical mixture, which showed an increased methanol yield compared with the homogeneous gas phase reaction in the reactor tube packed with quartz chips. The increased methanol yield has been attributed to the development of a co-operative effect between the Ga 2O 3 and MoO 3 oxide phases. The design approach has also been extended to the design of total oxidation of hydrocarbons for VOC destruction using benzene as a model VOC. In this case the design approach seeks to identify catalysts that can activate the substrate and the oxidant and also destroy the possible partial oxidation products. This approach is used to demonstrate that uranium oxide catalysts are extremely active for the oxidation destruction of hydrocarbons and chlorohydrocarbons. The degree of success from this approach indicates the validity of this novel approach in both the identification of selective and total oxidation catalysts.

98/03781 Studies of catalytic partial oxidation of methane to synthesis gas

The aetivities of Ni/Al2O3 and Pt-doped Ni/Al2O3 catalysts forpartial oxidation of methane to synthesis gas have been studied by using afixed-bed flow reactor It was found by examining the effects of dopedamount of Pt on catalytic properties of catalysts that the activity andselectivity for CO and H2 of Pt- doped Ni/Al2O3 were much better than thatof Ni/Al2O3 catalyst The interaction between Pt and Ni in the catalyst wasinvestigated by temperature-programmed reduction CO2-temperature programmed edsroption and CO-temperature-programmed desorption Theresults showed that Pt promoted the reduction of Ni and affected the CO andCO2 adsorption capacity of Pt-doped Ni-Al2O3 catalyst This indicated thatthere might be some strong interaction between Pt and Ni which enhancedthe activity and stability of Pt-dopedNi-Al2O3 catalyst.

The partial oxidation of methane to methanol: An approach to catalyst design

In this study a new approach for the design of catalysts for methane partial oxidation to methanol is outlined and results arising from this approach are discussed. The approach involves identifying metal oxide catalyst components which activate methane and oxygen, but do not readily destroy methanol, the desired product. A series of catalysts based on MoO 3 and WO 3 were prepared by impregnation with solutions containing the metal ions of the second component. The Cu/MoO 3 catalyst showed a selectivity advantage over the homogeneous gas phase oxidation in a reactor bed packed with quartz chips. In general, the WO 3 based catalysts were less effective for the production of methanol. Additionally, catalysts composed from physical mixtures of Ga 2O 3 and ZnO with MoO 3 were prepared. The Ga 2O 3/MoO 3 catalyst showed a maximum methanol yield greater than the homogeneous gas phase reaction over an inert bed of quartz particles. The increased methanol yield was attributed to a synergistic effect combining the beneficial reactivities of the MoO 3 and Ga 2O 3 component oxides. Comparison with data obtained from an empty reactor tube showed that none of the catalysts were as active or selective for methane partial oxidation to methanol.

FTIR spectroscopic investigation of the active sites on different types of silica catalysts for methane partial oxidation to formaldehyde

Several commercial silica samples showing different catalytic activities in the partial oxidation of methane (MPO) to formaldehyde have been investigated using FTIR technique. Two IR absorption bands at 893 and 909 cm−1, observed upon dehydroxylation of the silica catalysts and assigned to reactive siloxane sites on the surface (“strained siloxane bridges”), were found to disappear upon heating in methane at high temperature. The catalytic activity increases together with the intensity of the bands due to such “strained” sites in the different SiO2 samples.

Methane partial oxidation to methanol over Ga2O3 based catalysts: use of the CH4/D2 exchange reaction as a design tool

The CH4/D2 exchange reaction in used as an indication of methane activation over potential oxide catalysts; Ga2O3 exhibits an exchange rate over two orders of magnitude higher than other simple oxides and this approach leads to the identification of Ga2O3/MoO3 as a selective catalyst for methane partial oxidation to methanol.

An initial strategy for the design of improved catalysts for methane partial oxidation

The catalytic partial oxidation of methane to methanol has proved to be an extremely demanding reaction. It is clearly important that methanol should be stable over any potential catalysts, so a systematic study has been undertaken to determine the types of oxides over which methanol might have the required stability. The results should be valuable for the design of future catalysts. Methanol stability by catalytic oxidation has been investigated in the temperature range 150–500°C and 1 atm pressure. Over the majority of materials a substantial proportion of methanol was converted to carbon oxides below 350°C. Several oxides exhibited improved performance, these were MoO 3, Nb 2O 5, Ta 2O 5 and WO 3. Methanol conversion over these materials was high, but the major products were formaldehyde and dimethyl ether. Sb 2O 3 showed the best performance, producing a methanol conversion of only 3% at 500°C. The results have been compared with both physical and chemical properties of the oxides in an attempt to establish trends. In particular we have looked at relationships with oxygen exchange data. A weak but significant correlation between methanol decomposition to carbon oxides and the rate of oxygen exchange is discussed.