The nature of surface species on modified Pt-based catalysts for the SCR of NO by C<Subscript>3</Subscript>H<Subscript>6</Subscript> under lean-burn condition

The catalytic activity behavior for the selective catalytic reduction of NO by C₃H₆ under excess oxygen and the nature of surface species on the active sites of Pt/Al₂O₃ catalyst after adding a second metal (Fe, Sn, Co, Cr or W) were investigated. It has been found that an important role of second metals is on TONs of C₃H₆ and NO conversions and the nature of surface species produced on the catalyst surface at low temperature instead of the catalytic activity behavior towards the temperature programmed reaction. Although the introduction of each second metal distinctly disturbs the characteristic of surface species, the reaction mechanism is presumably similar. The observation of few surface species and the investigation about their reactivity indicate that few mechanisms are simultaneously proceeding at the same reaction condition.     

Flame sprayed tri-metallic Pt–Sn–X/Al2O3 catalysts (X = Ce,Zn, and K) for propane dehydration

Trimetallic nanocrystalline Pt–Sn–X/Al₂O₃ catalysts (X = Ce, Zn, and K) consisting of 0.3 wt.% Pt, 1 wt.% Sn, and 0.5 wt.% X have been prepared by one-step flame spray pyrolysis (FSP). As shown by the X-ray diffraction (XRD) and the transmission electron microscopy (TEM) results, the as-synthesized FSP-made catalysts were consisted of single-crystalline γ-alumina particles with average primary particle sizes 8 to 9 nm. The N₂ physisorption results revealed that all the catalysts contained only the macropore structure. The catalytic properties of the FSP-made catalysts were investigated in the dehydration of propane. Addition of Ce during FSP synthesis resulted in higher Pt dispersion as well as improved catalytic activity and stability than the non-promoted Pt–Sn/Al₂O₃. An opposite trend was found with the ones doped with Zn and K in which high surface coverage of Zn and K resulted in a significant loss of Pt active sites. The mechanism for the formation of the trimetallic nanoparticles during one-step FSP synthesis appeared to depend strongly on the differences in the vapor pressure of the metals and the alumina support in flame.     

Glycerol ethers synthesis from glycerol etherification with tert-butyl alcohol in reactive distillation

This paper presents a study of glycerol etherification with tert-butyl alcohol catalyzed by Amberlyst 15 in reactive distillation (RD). A thermodynamic analysis is firstly investigated by applying three group contribution methods, to determine the equilibrium composition by minimization of the Gibbs free energy and to compare the predicted values against measured data. Next, the kinetic model parameters are regressed by matching measured data from an autoclave reactor. The activity based Langmuir-Hinshelwood model is found to give the best representation of the reaction rate data. The regressed kinetic rate expressions are also compared against independently measured data in fixed bed reactors reported in the literature and found to give a good match. Finally, using the developed models, it is shown by simulation as well as verification by experiments, that the suitable RD configuration for the production of glycerol ethers in RD is the one consisting of 6 rectifying stages and 6 reaction stages without stripping stage.     

Characteristics and catalytic properties of Pt–Sn/Al2O3 nanoparticles synthesized by one-step flame spray pyrolysis in the dehydrogenation of propane

The Pt–Sn/Al₂O₃ catalysts with 0.3 wt% Pt and 0.5–1.5 wt% Sn loading were prepared by one-step flame spray pyrolysis (FSP). Unlike the catalysts prepared by conventional impregnation method, the FSP-derived catalysts were composed of single-crystalline γ-alumina particles with the as-prepared primary particle size of 10–18 nm and contained only large pores. The FSP catalysts exhibited superior catalytic activity and better stability than the ones made by impregnation in the dehydrogenation of propane, while they did not alter the selectivity to propylene (in all cases, propylene selectivity ≥96%). The presence of large pores in the flame-made catalysts not only facilitated diffusion of the reactants and products but could also lessen the amount of carbon deposited during reactions. As revealed by CO chemisorption, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), the metal particles appeared to be partially covered by the alumina matrix (Al–O) due to the simultaneous formation of particles during FSP synthesis. Such phenomena, however, were shown to result in the formation of active Pt–Sn ensembles for propane dehydrogenation as shown by higher turnover frequencies (TOFs).     

Effects of Co dopants and flame conditions on the formation of Co/ZrO2 nanoparticles by flame spray pyrolysis and their catalytic properties in CO hydrogenation

The Co/ZrO₂ catalysts with various Co loadings (5–10 wt.%) were prepared by one-step flame spray pyrolysis (FSP) under different flame conditions. As revealed by XRD and TEM, all the resulting Co/ZrO₂ nanoparticles were composed of single-crystalline particles exhibiting the characteristic tetragonal structure of ZrO₂. Varying the amount of Co dopants during FSP synthesis did not alter the primary particle size of ZrO₂ which was determined to be ca. 14 nm. On the other hand, increasing precursor feed rate from 3 to 8 ml/min resulted in an increase of ZrO₂ crystallite size from 10 to 19 nm. The higher precursor feed rate produced higher enthalpy of flame and longer residence times, which increased coalescence and sintering of the particles. Compared to the Co/ZrO₂ prepared by conventional impregnation method, the catalytic activities of the FSP-made catalysts were much higher. Moreover, the hydrogenation rates of the FSP-made Co/ZrO₂ catalysts were increased with increasing Co loading and precursor feed rate. According to H₂ chemisorption and H₂ temperature program reduction results, the improvement of catalytic activity and C₂–C₆ selectivities of the FSP-made catalysts in the CO hydrogenation was attributed to the higher number of Co metal active sites and lower interaction between Co/CoO and ZrO₂ support obtained via the FSP synthesis.     

Preparation and characterization of CeO2/TiO2 nanoparticles by flame spray pyrolysis

Nanocrystalline TiO₂, CeO₂ and CeO₂-doped TiO₂ have been successfully prepared by one-step flame spray pyrolysis (FSP). Resulting powders were characterized with X-ray diffraction (XRD), N₂-physisorption, Transmission Electron Microscopy (TEM) and UV-Vis spectrophotometry. The TiO₂ and CeO₂-doped TiO₂ nanopowders were composed of single-crystalline spherical particles with as-prepared primary particle size of 10-13 nm for Ce doping concentrations of 5-50 at%, while square-shape particles with average size around 9 nm were only observed from flame-made CeO₂. The adsorption edge of resulting powder was shifted from 388 to 467 nm as the Ce content increased from 0 to 30 at% and there was an optimal Ce content in association with the maximum absorbance. This effect is due to the insertion of Ce^3+/4+ in the TiO₂ matrix, which generated an n-type impurity band.     

New concepts in material and energy utilization

New criteria in material and energy utilization are proposed. The potential index (Θ*) is assigned to explain some natural processes in the world and to identify reasonably the preferable process instead of the efficiency. In addition, this term can first integrate the independent knowledge of the fields of mechanical, electrical and chemical engineering. It not only describes satisfactorily the transformation processes that are well-known in mechanical and electrical engineering, but also the increasing potential processes familiar in chemical engineering.     

Simultaneous enhancement of ethanol supplement in gasoline and its quality improvement

Ethanol and ethanol derivatives are attractive renewable energy resources nowadays. Even though ethanol can be blended directly into gasoline (called “gasohol”), many recent researches have reported disadvantages of gasohol. Apart from immiscibility and corrosion problems, overall air pollutant emissions from the use of gasohol are usually higher than those from the use of conventional gasoline because of its higher blending Reid vapor pressure (bRvp). Ethers derived from ethanol may overcome these drawbacks. Direct etherification of FCC gasoline with ethanol was investigated in this work. The reactions were carried out in a pressurized liquid phase reactor at 0.8 MPa and catalyzed by two commercial catalysts, i.e., β-zeolite and Amberlyst 16. The bRvp of etherified FCC gasoline was found to be lower than that of gasohol (20 vol.% ethanol), indicating that the gasoline from this process is more suitable than gasohol especially for the tropical zone or in summer. The decrease of bRvp was due to the consumptions of both ethanol and olefins. In case of β-zeolite catalyst, ethanol conversion was 36.3% while olefins content was decreased from 25.7 to 13.9 vol.%. However, as expected, etherified FCC gasoline gave slightly lower RON than gasohol. It was found that β-zeolite was a more suitable catalyst than Amberlyst 16 for the etherification of FCC gasoline with ethanol because it offered products with higher RON and higher ethanol conversion.     

Characterization and gene expression profiles of thermotolerant Saccharomyces cerevisiae isolates from Thai fruits

For industrial applications, fermentation of ethanol at high temperature offers advantages such as reduction in cooling costs, reduced risk of microbial contamination and higher efficiency of fermentation processes including saccharification and continuous ethanol stripping. Three thermotolerant Saccharomyces cerevisiae isolates (C3723, C3751 and C3867) from Thai fruits were capable of growing and producing 38 g/L ethanol up to 41°C. Based on genetic analyses, these isolates were prototrophic and homothallic, with dominant homothallic and thermotolerant phenotypes. After short-term (30 min) and long-term (12 h) exposure at 37°C, expression levels increased for the heat stress-response genes HSP26, SSA4, HSP82, and HSP104 encoding the heat shock proteins small HSP, HSP70, HSP90 and the HSP100 family, respectively. In isolates C3723 and C3867, expression was significantly higher than that in reference isolates W303 and TISTR5606 for TPS1 encoding trehalose-6-phosphate synthase, NTH1 encoding neutral trehalase and GSY1 encoding glycogen synthase. The results suggested that continuous high expression of heat stress-response genes was important for the long-term, heat stress tolerance of these thermotolerant isolates.     

Effect of dopants on the properties of metal-doped zirconia prepared by the glycothermal method

The effects of dopants on zirconia prepared via the glycothermal method were investigated by XRD to determine the crystal structure and crystallite size. Morphologies of products were observed by SEM. The basic sites of zirconia were studied by CO₂-temperature programmed desorption (CO₂-TPD). The functional group in the samples was determined using IR. The intensity of Zr³⁺, characterized by ESR, could be described as the oxygen coordinatively unsaturated Zr sites. The results suggest that doping elements can modify the surface chemistry of ZrO₂ to form hydroxyl groups and surface energies depending on the structure (cubic, tetragonal) in different dense phase. ESR peaks of Pb- and Bi-doped zirconia are different from the others, which showed high intensity of Zr³⁺.