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The catalytic combustion characteristics of methane-air mixtures in small-scale systems were investigated at elevated temperatures, with particular emphasis on identifying the main factors that affect formation and removal of combustion-generated pollutants. Computational fluid dynamics simulations were performed using detailed chemical kinetic mechanisms, and more insights were offered into the phenomena occurring in the temperature range where homogeneous and heterogeneous reaction pathways are both important. Reaction engineering analysis was performed to provide an in-depth understanding of how to achieve low emissions of pollutants. Spatial distributions of the major species involved were presented to gain insight into the interplay between the two competing pathways involved. The results indicated that the distribution of oxidized products depends critically on the feed composition, dimension, temperature, and pressure. Small-scale catalytic systems enable low emissions of pollutants even in a high temperature environment, along with high combustion efficiency. The interplay between the two competing pathways via radicals is strong, and the heterogeneous pathway can significantly inhibit the homogeneous pathway. The inhibiting effect also accounts for the low emissions of nitrogen oxides. Almost all of the nitrogen oxides emitted by small-scale catalytic systems are nitric oxide. Catalytic combustion technology can be used to reduce the formation of undesired products, especially pollutant nitrogen oxide gases far below what can be achieved without catalysts. Recommendations for the design of small-scale catalytic systems are provided.

The crystallization of molecular sieve ZSM-12 has been investigated by employing benzyltrimethylammonium chloride (BTMACl), tetraethylammonium bromide (TEABr) and methyltriethylammonium bromide (MTEABr) as templates. The crystallization of pure ZSM-12 framework was accomplished at Si/Al ratio of 90. The pure ZSM-12 samples so obtained were judged with respect to the differences in X-ray diffraction patterns, morphology, crystal size and total acidity to understand the role of template during crystallization. Interestingly, crystallization of ZSM-12 phase with rice, cubic and elongated cubic shaped morphology was favored in the presence of BTMACl, TEABr, and MTEABr, respectively. Finally, the effect of zeolite crystal size and morphology on hydroisomerization reaction was investigated by employing ZSM-12 (Si/Al = 90) based hydroisomerization catalysts. The performance of the prepared catalysts was judged in terms of their activity, selectivity and product distribution for the hydroisomerization reaction using n-hexadecane as a model feed. Based on the obtained results, the possible advantages of using a ZSM-12 sample of specific morphological features and crystal size for hydroisomerization of long chain n-paraffins are discussed. � 2013 Elsevier Inc. All rights reserved.

The crystallization of pure ZSM-12 phase was accomplished at Si/Al ratios ranging from 45 to 120 using tetraethylammonium bromide as the structure directing agent. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy, temperature programmed desorption of ammonia, and nitrogen adsorption-desorption measurements at 77 K, respectively. The well characterized samples were used to prepare Pt (0.5 wt%)/ZSM-12 hydroisomerization catalysts which were employed to perform n-hexadecane isomerization reaction. The catalysts were compared in terms of their activity, selectivity and product distribution at different conversion levels obtained through variation in temperature and residence times. Thus, obtained trend for product distribution over Pt/ZSM-12 system has been discussed in terms of framework Si/Al ratio to understand its role in determining the product selectivity. ZSM-12 with Si/Al ratio of 120 depicted the highest overall selectivity and favored mono-branching while those having Si/Al ratio of 45, 60 and 90 were found to favor mutlti-branching. � 2013 Springer Science+Business Media New York.

This study focuses on selective production of valuable chemicals from polystyrene (PS) via catalytic fast pyrolysis using micropyrolyzer-GC/MS set-up. Catalytic fast pyrolysis of PS was performed using eight different zeolites belonging to ZSM-5, zeolite-?, and zeolite-Y families. The catalysts were characterized for the strength of Br�nsted acid sites and pore size distribution. The composition of PS:catalyst was optimized at 1:2.3 � 0.2 wt./wt. to enhance the yield of benzene, at the same time reduce the yield of condensed ring fragments like indene and indane derivatives. The yields of various products correlated well with specific properties of zeolites like relative strength of Br�nsted acid sites, specific surface area, and pore volume. Importantly, the yield of benzene increased, while that of styrene, ?-methyl styrene, and dimers decreased with Br�nsted acidity. Zeolite-? hydrogen and zeolite-Y ammonia catalysts resulted in the formation of up to 50 wt.% of benzene. High temperatures led to a reduction in benzene yield and promoted the formation of styrene, ?-methyl styrene, and ethyl benzene. The observed product distribution with different zeolites and at different temperatures was corroborated using the relative importance of the primary protonation pathways involved in catalytic fast pyrolysis of PS. � 2015 Elsevier B.V.

The product distribution of electrochemical reduction of CO 2 can be altered by modifying the surface of pure copper by deposition. In this study, chronoamperometric deposition of Cu on Cu (Cu/Cu) was carried out at two different CuSO 4 bath concentrations, 0.25 M (high) and 0.025 M (low), termed as Cu/Cu-H and Cu/Cu-L respectively. These deposits were characterized by X-ray diffraction and they vary in their crystal orientation. Pure Cu and Cu/Cu were aligned towards (1 1 1) and (2 2 0) plane with a texture coefficient of 1.2 and 1.7, respectively. Electrodeposited electrodes were tested for the electrochemical reduction of CO 2 in KCl electrolyte and the results were compared with that of pure Cu electrode. Electrochemical reduction of CO 2 showed methane and ethane, with hydrogen as the byproduct. The product distribution varied with the crystal orientation of Cu electrodes. The maximum Faradaic efficiency of methane was 26% obtained on pure Cu electrode with (1 1 1) and (2 0 0) orientation, whereas Cu/Cu-L with dominating (2 2 0) orientation showed a maximum formation of ethane with Faradaic efficiency of 43%. A possible mechanism of product formation on Cu towards C 1 and Cu/Cu towards C 2 is also discussed.

Highly oxygenated fullerenes, C60On with 1 ≤ n ≤ 13, have been prepared by the Mo(O)2(acac)2 catalysed oxidation of C60 with tBuOOH. Increasing the catalystC60 ratio or increasing the reaction temperature increases the yield as well shifting the product distribution to higher oxygenated products, in contrast, increasing the tBuOOH concentration shifts the product distribution in the opposite manner. The MALDI mass spectra of reactions containing the highest oxygenated products (n > 5) show additional peaks (not observed for C60 under the same MS conditions) due to the cage-opened products Cx (x = 54, 56, 58) along with their oxygenated derivatives, CxOn (x = 54, 56, 58; n = 1-3). This journal is © The Royal Society of Chemistry 2013.

A critical review of the kinetics and selectivity of the Fischer–Tropsch synthesis (FTS) is given. The focus is on reaction mechanisms and kinetics of the water–gas shift and Fischer–Tropsch (FT) reactions. New developments in the product selectivity as well as the overall kinetics are reviewed. It is concluded that the development of rate equations for the FTS should be based on realistic mechanistic schemes. Qualitatively, there is agreement that the product distribution is affected by the occurrence of secondary reactions (hydrogenation, isomerization, reinsertion, and hydrogenolysis). At high CO and H2O pressures, the most important secondary reaction is readsorption of olefins, resulting in initiation of chain growth processes. Secondary hydrogenation of α-olefins may occur and depends on the catalytic system and the process conditions. The rates of the secondary reactions increase exponentially with chain length. Much controversy exists about whether these chain-length dependencies stem from differences in physisorption, solubility, or diffusivity. Preferential physisorption of longer hydrocarbons and increase of the solubility with chain length influences the product distribution and results in a decreasing olefin-to-paraffin ratio with increasing chain length. Process development and reactor design should be based on reliable kinetic expressions and detailed selectivity models.