Decrease In Methane Conversion Research Articles

Preparation of noble metal nanocatalysts and their applications in catalytic partial oxidation of methane

A series of noble metal catalysts (Ru, Rh, Ir, Pt, and Pd) supported on alumina-stabilized magnesia were prepared and employed in partial oxidation of methane. The prepared catalysts were characterized using BET, SEM, TEM and H2S chemisorption techniques. The results revealed that the Ru and Rh catalysts had the highest activity in catalytic partial oxidation of methane. Based on the obtained results the following order of activity was observed for different catalysts in partial oxidation of methane: Rh∼Ru>Ir>Pt>Pd. The obtained results also showed a high catalytic stability without any decrease in methane conversion up to 50h of reaction.

Preparation of Ni0.1Mg0.9O nanocrystalline powder and its catalytic performance in methane reforming with carbon dioxide

Ni0.1Mg0.9O nanocrystalline powders were prepared by surfactant assisted precipitation method and employed as catalyst in dry reforming. The powders were characterized by using XRD, BET, SEM, TGA/DSC and TPR techniques. The results showed that the surfactant to metal mole ratio affects the textural properties. Increasing in surfactant to metal mole ratio increased the specific surface area and decreased the crystallite and particle size. The Ni0.1Mg0.9O with the highest surface area (115.39m2g−1) was employed as catalyst in dry reforming. This catalyst showed a high catalytic activity and stability during 122h time on stream without any decrease in methane conversion.

Catalytic CO<sub>2</sub> Reforming of Methane over Perovskite Noble Metals

A series of perovskite-type oxides catalyst LaAl1-xNixO3 (0≤x≤1) and modified by substitute noble metal La0.4Al0.2Ni0.8M0.6O3 (M=Pt, Pd, Ru, Rh, Ir) prepared by the sol-gel method shows high activity, stability, good resistance to carbon deposition and sintering of the catalyst for the reforming of methane reaction. The reaction was studied under continuous flow using a mixture of CH4:CO2=1:1. Catalysts were characterized by using BET, XRD, SEM, EDS, and HR-TEM. The specific surface area of catalysts varied greatly from 3.07 to 10.18 m2/g with the different substitution (x) following calcination at 850°C. XRD analysis of the solids shows LaNiO3 and/or LaAlO3 as the main phases present on the solids depending on the degree of substitution and more intense peaks and cell parameters showed formation of Ni-Al solid solutions. SEM coupled to an energy dispersive X-ray spectrometer (EDS) shows the possibility to obtain a solid solution of LaAl1-xNixO3 (0≤x≤1) with propionic acid as solvent. The obtained results revealed that the Rh and Ru catalysts showed the highest activity and also showed a high catalytic stability without any decrease in methane conversion up to 3000min of reaction.

Combined dry reforming and partial oxidation of methane to synthesis gas on noble metal catalysts

In this paper CO 2 reforming of methane combined with partial oxidation of methane to syngas over noble metal catalysts (Rh, Ru, Pt, Pd, Ir) supported on alumina-stabilized magnesia has been studied. The catalysts were characterized by using BET, XRD, SEM, TEM, TPR, TPH and H 2S chemisorption techniques. The H 2S chemisorption analysis showed an active metal crystallite size in the range of 1.8–4.24 nm for the prepared catalysts. The obtained results revealed that the Rh and Ru catalysts showed the highest activity in combined reforming and both the dry reforming and partial oxidation of methane. The obtained results also showed a high catalytic stability without any decrease in methane conversion up to 50 h of reaction. In addition, the H 2/CO ratio was around 2 and 0.7 over different catalysts for catalytic partial oxidation and dry reforming, respectively.

CO2 reforming of CH4 over nanocrystalline zirconia-supported nickel catalysts

Mesoporous nanocrystalline zirconia with high-surface area and pure tetragonal crystalline phase has been prepared by the surfactant-assisted route, using Pluronic P123 block copolymer surfactant. The synthesized zirconia showed a surface area of 174m2g−1 after calcination at 700°C for 4h. The prepared zirconia was employed as a support for nickel catalysts in dry reforming reaction. It was found that these catalysts possessed a mesoporous structure and even high-surface area. The activity results indicated that the nickel catalyst showed stable activity for syngas production with a decrease of about 4% in methane conversion after 50h of reaction. Addition of promoters (CeO2, La2O3 and K2O) to the catalyst improved both the activity and stability of the nickel catalyst, without any decrease in methane conversion after 50h of reaction.

Oxidative coupling of methane over ternary metal oxide catalysts consisting of Groups I, III and V elements in the Periodic Table

Ternary metal oxides consisting of Group I (alkali metals)/Group III/Group V metals with an atomic ratio of 1:1:0.3 were prepared and their catalytic performance for the oxidative coupling of methane as well as their physicochemical properties were investigated. When adding Group V metals to Group I/Group III binary catalysts, a noticeable increase in the conversions of methane and oxygen was observed without any change in C 2+ selectivity. Of the ternary metal oxide catalysts, a Na/La/0.3Nb metal oxide showed the highest performance, viz. a methane conversion of 16.0% and a C 2+ selectivity of 74.1% at 1023 K under atmospheric pressure with a total gas flow-rate of 100 ml NTP/min ( CH 4/O 2molar ratio= 9 ). The stability test using a Na/La/0.2Nb catalyst, which was performed under the same conditions as above, showed that the catalyst was very stable with no decrease in methane conversion and C 2+ selectivity for more than 100 h. The crystalline structure, the surface composition and properties of base sites of Na/La/Nb oxide catalysts were investigated using X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) of carbon dioxide. The catalytic performance of the Na/La/Nb mixed oxides depended on the ratio of the two crystalline phases of La 2O 3 and La 3NbO 7. When sodium was added to La 2O 3 with a La/Na ratio of 1, new base sites were produced, resulting in an increase in the C 2+ selectivity with a significant decrease in methane conversion. The methane conversion was increased by adding a small amount of niobium to the Na/La catalyst, resulting in a change of part of the La 2O 3 to La 3NbO 7. However, when all of the La 2O 3 was changed to La 3NbO 7, the C 2+ selectivity decreased due to the lack of new base sites. A good balance of both crystals (La 2O 3 and La 3NbO 7) may be obtained at a Nb/Na atomic ratio of 0.15–0.3, which optimizes the catalytic performance of the mixed oxides.

Conversion of methane to methanol by catalytic supercritical water oxidation

Selective conversion of methane to methanol has been accomplished by catalytic partial oxidation over C r2O 3 in supercritical water (SCW). The presence of water in high concentration inhibits the methane conversion but promotes the yield of methanol. The methane oxidation reaction was observed to be slightly negative order in oxygen concentration; increasing oxygen concentration produced a small decrease in methane conversion. Methanol oxidation was positive order in oxygen concentration; thus, increasing oxygen concentration dramatically reduced the yield of methanol. A consistent set of reaction pathways are developed and rate constants, which accurately model the experimental results, are calculated.