Catalytic Activity For Methane Combustion Research Articles

Phase transformation and catalytic activity of hexaaluminates upon high temperature pretreatment

Both hexaaluminates powder have been synthesized with the co-precipitation method. High temperature pretreatment catalysts are characterized by X-ray diffraction (XRD) and BET method. The catalytic activity in methane combustion also is reported. The hexaaluminate structure is formed and retains the surface area of 20–30 m 2/g upon calcinations at 1200 °C for both SLMA (Sr 0.8La 0.2MnAl 11O 19) and SBLMA (Sr 0.3Ba 0.5La 0.2MnAl 11O 19). The surface area of SBLMA is larger than that of SLMA upon temperature higher than 1200 °C illustrating the superior thermal stability of the barium hexaaluminate. Partial replacement of Sr 2+ ion with Ba 2+ ion improves the thermal stability of the Ba-containing system. Also, the high surface area for SBLMA can be understood from the microstructural change of pore size. The SBLMA possesses larger pore than the SLMA to resist sintering under high temperature aged and shows a good activity in methane combustion.

Catalytic combustion properties of nanocomplex oxide for natural gas*

Abstract The catalysts of copper oxide supported on cerium dioxide were prepared by different methods for methane catalytic combustion. The effects of copper content in the catalysts and calcination temperatures of the catalysts on the catalytic activity are investigated. Results show that the complex oxide catalyst exhibits high catalytic activity for methane combustion due to the synergistic effect of CuO and CeO2. The catalyst prepared by impregnation is more active than that prepared by controlled coprecipitation even if CuO content is the same. When W (CuO)<13%, the light-off temperature and full conversion temperature for the CH4 reaction decrease with the increasing of CuO content in the catalysts. However, when the copper content is above 13%, the excess CuO has a negative effect on the catalytic activity owing to the formation of bulk CuO particles. A proper calcination temperature of 650°C can lead to a high dispersion of CuO and accordingly can enhance the catalytic activity of the composities....

Formation of a Novel Type of Reverse Microemulsion System and Its Application in Synthesis of the Nanostructured La0.95Ba0.05MnAl11O19 Catalyst.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The Preparation and Characterization of Highly Dispersed PdO over Alumina for Low?temperature Combustion of Methane

PdO/Al2O3 catalysts prepared by glow discharge plasma treatment followed by thermal calcination show a much higher dispersion and a better catalytic activity for methane combustion at relatively low temperatures. The dispersion of palladium active species by such plasma prepared catalysts is 29.7%, 5.4 times higher than that of conventional catalysts. XPS analysis indicates that a surface enrichment of Pd active species (PdO) has been achieved after plasma treatment. The surface atomic composition of PdO of plasma prepared catalysts reaches 10.5%. XRD characterization also confirms a well‐crystallized PdO phase present on the plasma prepared catalyst. The light‐off temperature of the plasma prepared catalyst is 370°C, 50°C lower than that obtained from the conventional catalyst.

Low-Temperature Combustion of CH4over CeO2–MOxSolid Solution (M = Zr4+, La3+, Ca2+, or Mg2+) Promoted Pd/γ–Al2O3Catalysts

The catalytic behavior of Pd (2 wt%) catalysts supported on γ-Al2O3 and promoted with CeO2 − MOx(M = Zr4+, La3+, Ca2+, or Mg2+) solid solution was investigated for methane combustion. The results demonstrated that Pd/γ-Al2O3CeO2 MOx catalysts can be effective for the low-temperature catalytic combustion of methane and are comparable in activity to other conventional catalysts for this reaction. The XPS and XRD results indicated that an enhanced mobility of lattice oxygen induced by the perturbation of Ce–O lattice was responsible for an increased catalytic performance during oxidation reaction. The most active sites in the catalyst system involve contacts between Pd and the CeO2–MOx mixed oxide component. Meanwhile, pre-treatment conditions have significant effect on the catalytic activity in methane combustion.

Formation of a novel type of reverse microemulsion system and its application in synthesis of the nanostructured La0.95Ba0.05MnAl11O19 catalyst.

In the study, a novel microemulsion system, consisting of water, iso-propanol and n-butanol, was developed to synthesize the nanostructured La(0.95)Ba(0.05)MnAl(11)O(19) catalyst with high surface area and catalytic activity for methane combustion.

Sol-gel titania modified with Ba and Li atoms for catalytic combustion

Samples of compounds in the ternary system BaO-Li2O-TiO2 were synthesized by using the sol-gel method at pH 3 and pH 9, and the calcination temperatures of 600 and 800°C in the region of solid solutions which can form the “ideal” composition Ba3Li2Ti8O20. The X-ray diffraction patterns of the samples showed a mixture of three crystalline phases, the main one was isostructural with the ternary phase Ba3Li2Ti8O20; the other two were BaTiO3 and Li2TiO3. By refining the structures with the Rietveld technique, a good fit to the experimental diffraction pattern was found, showing the partial substitution of Ti by Li in the Ba2Ti6O13 structure. The catalytic activity in methane combustion under the stoichiometric mixture of dilute CH4/O2 was higher for the samples calcined at 600°C, where the Ba3Li2Ti8O20 ternary compound was formed. This high activity can be related with the large specific surface area, presence of anatase and low crystallite size.

Catalytic combustion of methane over bimetallic catalysts a comparison between a novel annular reactor and a high-pressure reactor

The effects of adding a co-metal, Pt or Rh, to Pd/γ-Al 2O 3 catalysts were studied with respect to the catalytic activity for methane combustion and compared to a Pd/γ-Al 2O 3 catalyst, using both a pressurized pilot-scale and a lab-scale annular reactor. Temperature programmed oxidation (TPO) experiments were also carried out to investigate the oxygen release/uptake of the catalyst materials. Palladium showed an unstable behavior both in the pilot and lab-scale experiments at temperatures well below the PdO to Pd transformation. An addition of Pt to Pd stabilized, and in some cases increased, the catalytic activity for methane combustion. The TPO experiments showed that the oxygen release peak was shifted to lower temperatures even for low additions of Pt, i.e. Pd:Pt=2:1. For additions of rhodium only small beneficial effects were seen. The steady-state behavior of the lab-scale annular reactor correspond well to the pressurized pilot-scale tests.

The catalytic activity and surface characterization of Ln 2B 2O 7 (Ln=Sm, Eu, Gd and Tb; B=Ti or Zr) with pyrochlore structure as novel CH 4 combustion catalyst

Ln 2B 2O 7 (Ln=Sm, Eu, Gd and Tb; B=Zr or Ti) with pyrochlore structure was prepared by sol–gel method for the high-temperature catalytic combustion. The crystal structure of Ln 2B 2O 7 was identified by XRD and their surface area was about 4 m 2/g after calcinations at 1200 °C. Catalytic activity of methane combustion was observed for Ln 2Zr 2O 7 series and the best catalyst was Sm 2Zr 2O 7. Its relative reaction rate per unit surface area at 600 °C was 2 cm 3/m 2 min, which was twice higher than that of Mn-substituted Sr hexaaluminate. From surface analysis by XPS, the low binding energy of each Ln element of Ln 2Zr 2O 7 compared to that of Ln 2Ti 2O 7, gave the catalytic activity of methane combustion.

Preparation of Mn substituted La-hexaaluminate catalysts by using supercritical drying

LaMn x Al 12− x O 19 catalysts were prepared from NH 4OH and metal nitrates solutions. Supercritical drying (SCD) and conventional oven drying (CD) methods were used to extract the water in the hydrogel. The effects of drying methods on properties of the catalysts were investigated by means of TEM, N 2-adsorption, thermogravimetry (TG)–differential thermal analysis (DTA) and X-ray diffraction. SCD method is beneficial to maintain high surface area and improving catalytic activity for methane combustion of the catalyst. The specific surface area and pore volume of LaMn 1Al 11O 19 catalyst prepared by SCD method are 28 m 2/g and 0.23 cm 3/g, respectively, and the ignition of methane could be carried out at 450 °C. However, those of the CD catalyst prepared from the same precursor are 15 m 2/g, 0.11 cm 3/g and 530 °C, respectively. Suitable Mn content (0≤ x≤2) could promote the formation of LaMnAl 11O 19 hexaaluminate, while further addition of Mn (2< x≤6) cause the formation of LaMnO 3.

Reduction property and catalytic activity of Ce 1− XNi XO 2 mixed oxide catalysts for CH 4 oxidation

Ce 1− X Ni X O 2 oxides with X varying from 0.05 to 0.5 were prepared by different methods and characterized by XRD and TPR techniques. Ce 0.7Ni 0.3O 2 sample prepared by sol–gel method shows the highest reducibility and the highest catalytic activity for methane combustion. Three kinds of Ni phases co-exist in the Ce 1− X Ni X O 2 catalysts prepared by sol–gel method: (i) aggregated NiO on the support CeO 2, (ii) highly dispersed NiO with strong interaction with CeO 2 and (iii) Ni atoms incorporated into CeO 2 lattice. The distribution of different Ni species strongly depends on the preparation methods. The highly dispersed NiO shows the highest activity for methane combustion. The NiO aggregated on the support CeO 2 shows lower catalytic activity for methane combustion, while the least catalytic activity is found for the Ni species incorporated into CeO 2. Any oxygen vacancy formed in CeO 2 lattice due to the incorporating of Ni atoms adsorbs and activates the molecular oxygen to form active oxygen species. So the highest catalytic activity for methane combustion on Ce 0.7Ni 0.3O 2 catalyst is attributed not only to the highly dispersed Ni species but also to the more active oxygen species formed.

Improvement of the Pd/Al2O3 Catalyst by the Control of the Sol-Gel Preparative Parameters

In this work, the metal dispersion of the Pd/Al2O3 catalyst prepared by sol-gel method is improved by an adequate optimisation of the preparative variables. First, the gelation temperature and the ageing time are selected, in order to avoid the reduction of the metal precursor (palladium acetylacetonate, Pd(acac)2) by the solvent (sec-butanol, sB). The metal sintering effect on the catalysts treated in oxygen at 500°C is then minimized when the alumina pore size is controlled by the variation of the alumium alkoxide (AsB) concentration and the acetic acid amount ([AcA]/[AsB]). The appearance of new palladium particles on the alumina surface and the matching between the particle diameters and the pore sizes were also effective for the metallic surface area improvement on the samples treated in oxygen at 800°C. Compared to the reference catalysts, the higher metal dispersion obtained on the sol-gel ones was the determinant factor for their higher catalytic activity in methane combustion.

An Experimental Study of Non-Uniform Pd Catalytic Monoliths

Palladium was deposited in monoliths by chemical vapour deposition (CVD) using Pd(acac) 2 as precursor. A decreasing axial palladium distribution profile was obtained. The monoliths exhibited catalytic activity for methane combustion and had decreasing axial temperature profiles for the experimental conditions employed. A catalytic monolith prepared by impregnation with the same precursor showed increasing axial temperature profile, and overall temperature gradient was larger than that of monoliths prepared by CVD. Reactant conversion was higher for the CVD catalyst than the impregnated one for the same inlet conditions and total palladium loading.

Methane combustion over supported cobalt catalysts

A series of cobalt-based catalysts with different supports have been prepared using impregnation method, and characterised by X-ray diffraction (XRD), laser Raman (LR), and infrared spectroscopy (IR). The catalytic activities for methane combustion were assessed in a micro-reactor. The ZrO 2 and Al 2O 3 supports are themselves active in methane combustion, and ZrO 2 supported cobalt catalyst was found to have the highest activity amongst the TiO 2, Al 2O 3, MgO supported catalysts and bulk Co 3O 4. The Co content has a marked effect on the activity of the ZrO 2 supported catalyst with 1.0 and 15 wt.% of Co having the lowest light-off temperature in methane combustion. In the MgO supported catalyst, Co oxide was highly dispersed over the MgO support surface or enters the lattice of MgO to form a solid solution, whose activity for methane combustion is reasonable. The zirconia supported cobalt catalysts are very active and stable when calcination or reaction temperature is no more than 900°C. Calcining the catalysts at temperatures above 900°C for more than 1 h decreases the catalyst activity. The deactivation of the catalyst probably results from the decrease of the surface area.

Catalytic Combustion of Methane over Cobalt–Magnesium Oxide Solid Solution Catalysts

A series of cobalt–magnesium oxide solid solution catalysts (CoMgO) have been prepared using urea combustion methods, and characterised by X-ray diffraction (XRD) and laser Raman (LR). The catalytic activities for methane combustion have been tested in a continuous-flow microreactor. The Co content has a significant effect on the activity of the cobalt–magnesium oxide solid solution catalysts. The catalysts containing 5 and 10% Co have the lowest light-off temperature in methane combustion. In the preparation of cobalt–magnesium oxide solid solution catalysts, higher urea to metal ratio favors the formation of the catalysts with smaller crystal particles and leads to a better catalytic performance for methane combustion. Addition of lanthanum nitrate to the solution of Co and Mg nitrate depressed the formation of the cobalt–magnesium oxide solid solution and decreased the activity of the catalysts for methane combustion. The cobalt–magnesium oxide solid solution catalysts are very stable when the calcination or reaction temperature is no more than 900°C. However, the catalytic activity decreases rapidly after high temperature (>1000°C) calcination, possibly due to sintering of the catalyst and thus decrease of the surface area.

Thermal Stability of Perovskite-Based Monolithic Reactors in the Catalytic Combustion of Methane

Perovskite-based monolithic reactors have been studied for methane catalytic combustion. Monoliths have been prepared by washcoating cordierite honeycomb substrates with lanthanum-stabilized γ-Al2O3, on which LaMnO3 is dispersed. Scanning electron microscopy analysis showed a homogeneous distribution of LaMnO3 on the washcoat, which, after repeated aging cycles at 1100 °C, is still well anchored to cordierite. The catalytic activity in methane combustion is very promising, even higher than that measured on the corresponding catalyst powders with the same chemical composition. Isothermal catalytic activity measurements reveal that the first aging cycle slightly reduces the activity of fresh catalyst, while further repeated aging treatments do not deactivate the monolithic reactor. In autothermal conditions, the monolithic catalyst is able to ignite a mixture of CH4 (3% vol) and O2 (10%) at an inlet gas temperature of about 500 °C, giving complete methane conversion and negligible CO and NOx emissions. More...

Effect of Preparation Conditions on the Stability of Pt/Al2O3 Catalysts in Methane Combustion

Alumina supported platinum catalysts were prepared by sol-gel method using aluminum-sec-butoxide, platinum acetylacetonate and sec-butanol. Various gelation process were performed either by the help of a gelation agent (water or acetic acid) or by a slow condensation without hydrolysis source. The textural and the structural study of the catalysts using the nitrogen physical adsorption and the hydrogen chemisorption showed that the BET surface area and the metal dispersion varied when the hydrolysis and the gelation processes were modified. The catalytic activities for methane combustion performed on the fresh and aged catalysts were correlated to the metal dispersion values. In addition the catalytic activity loss under reaction mixture seemed to be caused by the metal dispersion decrease. When the catalysts were aged under the reaction mixture at 600°C for 72 h, a BET surface area decrease and a metallic surface area loss were observed. The resistance to sintering observed to be dependant on the hydrolysis and the gelation processes was in favor of the catalyst prepared by acetic acid.

Effects of addition of Pt to PdO/Al 2O 3 catalyst on catalytic activity for methane combustion and TEM observations of supported particles

Effects of addition of Pt to PdO/α-Al 2O 3 catalyst on the catalytic activity for methane combustion have been investigated. The size distributions and the shapes of supported particles in catalysts and their behavior at high temperature were measured. The results were discussed in relation with the heat resistance of supported particles. Supported particles were characterized by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The addition of Pt to PdO/α-Al 2O 3 catalyst did not only bring about the increase of catalytic activity, but it was also effective for preventing the catalyst deactivation in methane combustion. These effects were attributed to the higher dispersion of the supported particles and the suppression of the particle growth. From the in situ observation of the PdO/α-Al 2O 3 catalyst, it was clarified that the supported particles migrated and then coalesced with each other like dewdrops on the surface of α-Al 2O 3 support at the temperature range from 843 to 863 K. The particle growth of supported particles proceeded through the migration and coalescence of crystallites. On the other hand, with the Pt-added catalyst, the migration and coalescence of supported particles were not observed. Its EDS analysis revealed that the every supported PdO particle contained Pt. The supported PdO particles containing Pt have smaller contact angles and are flatter than PdO particles free from Pt.

Catalytic combustion of methane on copper-substituted barium hexaaluminates

Barium hexaaluminates partially substituted by copper have been synthesized by a sol–gel method. Formation of the parent BaAl12O19 and the mixed BaCuAl11O18.5 catalysts occurred during calcination at 1200°C. XRD showed a good crystallinity of the structure and expansion of the unit cell parameter due to the presence of larger mathrmCu2+ ions in place of Al 3+ in tetrahedral sites. The presence of copper strongly enhances the catalytic activity in methane combustion, which should be due to the Cu2+ species evidenced by FTIR of adsorbed CO and by TPR. The introduction of a second copper ion in the structure was not possible, however, as revealed by the formation of copper (II) aluminate in addition to the Cu-substituted hexaaluminate phase.

Synthesis, structure and catalytic properties of Fe-substituted barium hexaaluminates

A sol–gel method using Ba and Al isopropylates and iron nitrate has been used to synthesise barium hexaaluminate partially substituted with iron. After calcination under oxygen at 1200°C the β-alumina structure was obtained. Formation of the mixed BaFexAl12-xO19 phase occurred for x=1–4. XRD measurements showed a good crystallinity of the structure and expansion of unit cell parameters due to the presence of larger Fe3+ ions substituting Al3+ ones in octahedral sites only. Mossbauer spectroscopy revealed that Fe3+ ions are present in four different octahedral sites slightly distorted. Catalytic activity in methane combustion showed that an optimum was obtained for solid containing 2 Fe ions per unit cell: the increase of the amount of introduced iron was counterbalanced by the decrease of specific surface area. Intrinsic activities have been calculated for the four solids in both the fresh and aged states. It is observed that increasing iron content increases relative activities in the same ratio as the populations of iron located in two sites as deduced from Mossbauer spectroscopy. It is then tentatively assumed that activity is attributed to octahedrally coordinated Fe3+ ions in some specific sites.