Natural gas conversion remains one of the essential technologies for current energy needs. This review focuses on the mechanistic aspects of the development of efficient and durable catalysts for two reactions, carbon dioxide reforming and the oxidative coupling of methane. These two reactions have tremendous technological significance for practical application in industry. An understanding of the fundamental aspects and reaction mechanisms of the catalytic reactions reviewed in this study would support the design of industrial catalysts. CO2 reforming of methane utilizes CO2, which is often stored in large quantities, to convert as a reactant. Strategies to eliminate carbon deposition, which is the major problem associated with this reaction, are discussed. The oxidative coupling of methane directly produces ethylene in one reactor through a slightly exothermic reaction, potentially minimizing the capital cost of the natural gas conversion process. The focus of discussion in this review will be on the attainable yield of C2 products by rigorous kinetic analyses.
Well-ordered mesoporous materials have attracted a great deal of attention because of their controllable structures and compositions, which make them suitable for a wide range of applications in catalysis, environmental clean-up, and development of advanced materials. In general, the mesoporous materials can be synthesized based on the self-assembly of surfactants and inorganic precursors. In addition to the use of the surfactants including cationic and nonionic surfactants, a synthesis route for preparing mesoporous silicas using anionic surfactants has been developed by using aminosilane or quaternized aminosilane as a co-structure-directing agent. Thus obtained “anionic surfactant templating mesoporous silica” (AMS) is synthetically interesting not only for their structural diversity but also for the opportunity to functionalize the pore surface. The removal of the surfactant from the so-called “as-synthesized” AMS by solvent extraction results in the mesoporous silica with aminopropyl groups intact. Thus obtained amino-functionalized AMS can be applied to solid-base catalysis, adsorption, drug delivery, etc. Besides well-known surfactant-templating route, a silica material having three-dimensionally ordered mesopores can be also obtained via a hard-sphere packing (HSP) route based on the formation of a colloidal array of uniform-sized silica spheres. A novel and simple liquid-phase method for forming uniform-sized silica nanospheres (SNSs) has been developed by using basic amino acid as a base catalyst for hydrolysis of tetraethyl orthosilicate Si(OC2H5)4. The size of SNSs can be tuned ranging from 8 to 550 nm by employing the seed regrowth method. Interestingly, the arrangement of SNSs into the cubic closed packed (ccp) structure was achieved simply by solvent evaporation. The thus-formed colloidal array of SNSs has three-dimensional interparticle voids with high uniformity in size, and can be categorized into well-ordered mesoporous silicas.
After the primary production period, water flooding is usually performed to recover more oil from reservoirs. However, water flooding recoveries are low from naturally fractured carbonate reservoirs, due in part to these reservoirs being mixed to oil-wet. Most of Iranian reservoirs are naturally fractured. Chemical process and especially surfactant flooding is an interested method because of its effect on interfacial tension (IFT) reduction and wettability alteration. Different surfactants are used for chemical flooding in the world but these chemical have high price and some detrimental effect on the environment. In this paper a new nonionic biosurfactant which is produced from the leaves of special tree called Zizyphus Spina-Christi is introduced. There is a hypothesis that this surfactant can be used in chemical flooding of fractured reservoirs because of very low cost and availability in Middle-East and Africa compared to other currently used surfactants. For this purpose surfactant is extracted from the leaves by spray dryer method. The pendant drop method is used to measure interfacial tension and critical micelle concentration (CMC) values. In order to investigate the effect of this surfactant on oil recovery two series of imbibition experiments are conducted on water-wet and oil-wet samples. It is observed that oil recovery is about ∼16 % OOIP (original oil-in-place) for oil-wet cores by using this surfactant. In the same test, no oil is produced with water due to high oil wettability. After adding surfactant to the water, the oil recovery about ∼7 % OOIP is obtained. Other test is done on water-wet cores which shows that addition of surfactant reduce the ultimate recovery from ∼35 % OOIP to ∼12.5 % OOIP. Reducing interfacial tension cause decrease in imbibition drive mechanism and lower the ultimate recovery. These results indicate that this new type of surfactant can meet the technical requirements as enhanced oil recovery (EOR) agent for chemical flooding.
Butadiene demand is expected to increase rapidly, particularly in developing countries. We developed a new production process of butadiene that will allow suppliers to produce sufficient amount of butadiene. In this study, we focused on n-butane dehydrogenation, and evaluated the activity of Pt–Sn catalysts supported on Fe2O3–Al2O3, ZnO–Al2O3 and MgO–Al2O3 prepared by the co-precipitation method. Pt–Sn/MgO–Al2O3 (Mg/Al = 1/2) showed the highest activity and butadiene yield. Support composition of MgO–Al2O3 influenced the catalyst activity. The catalysts underwent deactivation owing to coke deposits over the catalyst, and their activity was recovered after regeneration treatment. Addition of Mg was effective in suppressing coke formation, as revealed by TG-DTA analysis. Reaction temperature and Sn/Pt molar ratio were changed effectively in order to increase the butadiene yield, and the results showed that Sn suppresses the side reaction over the support surface. Sintering of Pt particles was inhibited by the addition of Mg and Sn.
Synthesis isoparaffins from light naphtha was studied using n-hexane conversion. The main target products were multi-branched isoparaffins. Which are harder to form than mono-branched isoparaffins in the zeolitic pores. Nano-technology was applied to form composites of zeolites and nano-sized (defined as 5-50 nm, and here called ns) oxides, to improve the state of metal species for isomerization into multi-branched isoparaffins. Skeletal isomerization of n-hexane was advanced, based on catalyst optimization with 0.1-2 wt% Pt or Pd on 35 wt% ns Al2O3 or ns SiO2 and 65 wt% H-BEA zeolite (SiO2/Al2O3 = 16-39). The presence of ns Al2O3 in the catalyst increased the mechanical strength of the shaped zeolite catalyst and reformed the surface acidity of the zeolite to milder acid suitable for skeletal isomerization without cracking. X-ray photoelectron spectroscopy showed that the nano-alumina dispersed and combined to the anisotropic surface of BEA zeolite to form an ionic and highly developed surface for palladium dispersion to improve the catalyst activity and selectivity.
In order to develop the preparation procedure for silicomolybdic acid (H4SiMo12O40, SMA) on silica catalysts, H2MoO4 and excess tetraethylorthosilicate (TEOS) are employed as starting reagents and three catalysts with different loadings are prepared by a hydrothermal sol-gel method. From Raman measurements in the course of the preparation steps, Raman spectra imply the formation of beta type silicomolybdic acid (β-SMA) reported by M. A. Bañares et al.; Raman spectroscopy suggests that the SMA species are formed in the precursor solution and is stable on 14.6 and 20 wt% MoO3/SiO2 even in the drying process (110 °C). When the loading is 7.9 wt%, Raman peaks of SMA disappear after the hydrothermal treatment at 100 °C. The structural distortion of the SMA due to hydrogen interaction between OH groups and Mo=O bonds is also observed. Raman measurement indicates the transformation to β- and α-MoO3 in 20 wt% MoO3/SiO2 after the calcination at 500 °C, but only surface molybdates are observed at the loadings of 7.9 and 14.6 wt%. The results indicate that H2MoO4 is also effective for the simple preparation of SMA. In addition, as no XRD patterns of all Mo species are observed, Raman spectroscopy is an effective method to structural analysis of Mo species, even in liquid and wet samples.
The kinetic study on the effect of O2 concentration in the selective catalytic reduction (SCR) of nitrogen oxide (NOx) by ammonia (NH3) was systematically carried out at temperatures below 200 °C over Fe- and Cu-loaded beta zeolites. The large difference was observed in the effect of O2 concentration over the two catalysts: for the Fe-loaded beta zeolite, the NO conversion increased considerably with the O2 concentration. On the other hand, for the Cu-loaded beta zeolite, increasing the concentration of O2 did not have a significant impact. In addition, the temperature dependence of the apparent reaction orders was investigated. The apparent reaction order of O2 decreased with an increase in the reaction temperature, being 0.9 at 150 °C and 0.4 at 200 °C for the Fe-loaded beta zeolite, and 0.2 at 125 °C and 0.1 at 175 °C for the Cu-loaded beta zeolite. The fact that the degree of the reduction in the reaction order of O2 was consisted with that of the increase in the reaction order of NH3 when the reaction temperature was increased strongly suggests that adsorbed NH3 inhibits the adsorption of O2.
Carburized Cs0.2Ni0.8/ZrO2 catalyst is useful for the steam reforming of ethanol (ethanol : water =1:13) at 773 K to produce hydrogen at 1.95 mmol/min/g-cat during 60 h, with 82 % CO2 selectivity with trace amounts of CO and CH4. The cesium addition to the Ni/ZrO2 catalyst resisted the carbon deposition, kept more reducing Ni carbide and produced highly hydrogen.
Catalytic fast pyrolysis of two kinds of Jatropha residues and cryptmeria with USY zeolite were performed by using Pyrolyzer-GC/MS system. Large amount of aromatic hydrocarbons were produced by pyrolysing with low-silica USY zeolite (SiO2/Al2O3=10 mol/mol) from two kinds of Jatropha residues though small amount of them were produced from Cryptomeria.
We found that LaInO3 perovskite catalyst showed high activity for oxidative coupling of methane (OCM). Partial substitution of La3+ site in the LaInO3 catalyst with Ba2+ increased its catalytic activity and selectivity to C2 hydrocarbons drastically. The partial substitution of La3+ site in LaInO3 with Ba2+ increased oxygen vacancies in the stable cubic phase, and then contributed to the production of active oxygen species on its surface for selective C2 formation.