Gas-phase dehydration of glycerol over commercial Pt/γ-Al2O3 catalysts

Gas-phase dehydration of glycerol to produce acrolein was investigated over commercial catalysts based onγ-Al2O3, viz. A-64, A-56, I-62, AP-10, AP-56, AP-64 and KR-104. To understand the effect of Cl?anions, HCl-impregnated sup-ports have been investigated in the dehydration reaction of glycerol at 375 °C. For comparison, various H-zeolites were also examined. It was found that the glycerol conversion over the solid acid catalysts was strongly dependent on their acidity and surface area. And the relationship between the catalytic activity and the acidity of the catalysts was discussed. The outstanding properties of Pt/γ-Al2O3 catalyst systems for the dehydration of glycerol were revealed. Pt/γ-Al2O3 catalyst (AP-64) showed the highest catalytic activity after 50 h of reaction with an acrolein selectivity of 65%at a conversion of glycerol of 90%. Based on these results, catalysts based onγ-Al2O3 appear to be most promising for gas phase dehydration of glycerol.     

Catalytic Oxidative Decomposition of Hydrazine in Vapor Phase over Nanosized Au/γ‐Al2O3

The catalytic activity of nanosized Au/γ‐Al₂O₃, synthesized by a deposition‐precipitation process, on oxidative decomposition of hydrazine in air is discussed. The catalyst exhibited an excellent activity at low temperatures. The activity was strongly dependent upon the gold cluster size. The impacts of certain pertinent operating parameters including the particle size of the catalyst, temperature, hydrazine concentration, and feed flow rate on the extent of the reaction were investigated. The results were reproducible with a mean absolute deviation of 3 %. Deactivation of the catalyst during the reaction was found to be unlikely. Finally, a kinetic model based on the Eley‐Rideal formulation was proposed for the reaction and a correlation was made between the data predicted from the model and those determined experimentally.     

Oxidation Kinetics of Carbon Deposited on Cerium‐Doped FePO4 during Dehydration of Glycerol to Acrolein

A cerium‐doped FePO₄ catalyst dehydrates glycerol to acrolein in the gas phase but carbon accumulation reduces the reaction rate with time. Reaction rates may be maintained for longer times by co‐feeding low concentrations of oxygen together with the glycerol, but the acrolein yield drops proportionally to the oxygen concentration. The catalyst is easily regenerated by air and the reaction rate is proportional to both the oxygen concentration and quantity of carbon. The carbonaceous deposits may be due to both glycerol and acrolein: when either is fed to the catalyst, the CO₂/CO ratio is close to 1; during the regeneration step, the CO₂/CO ratio is near 4. A kinetic model of first order in both oxygen concentration and adsorbed sites characterizes the transient data very well.     

Continuous Hydrogenation of Toluene over Sr‐ and PEG800‐Modified Ni/γ‐Al2O3 Catalysts

A series of γ‐Al₂O₃‐supported nickel‐based catalysts were evaluated in continuous hydrogenation of toluene. Sr‐ and poly(ethylene glycol) 800 (PEG800)‐modified Ni/γ‐Al₂O₃ catalysts provided the best activity with high conversion of toluene and selectivity for methylcyclohexane which was ascribed to the addition of Sr and PEG800 during the preparation process, resulting in smaller and highly dispersed Ni species on the surface and in the pores of γ‐Al₂O₃. Furthermore, the formation of SrCO₃ and NiAl₂O₄ is believed to be advantageous for the dispersion and stabilization of the active Ni species, accounting for its good stability.     

Thermal degradation of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) as studied by TG,TG–FTIR,and Py–GC/MS

The thermal degradation kinetics of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [poly(HB–HV)] under nitrogen was studied by thermogravimetry (TG). The results show that the thermal degradation temperatures (T_o, T_p, and T_f) increased with an increasing heating rate (B). Poly(HB–HV) was thermally more stable than PHB because its thermal degradation temperatures, T_o(0), T_p(0), and T_f(0)—determined by extrapolation to B = 0°C/min—increased by 13°C–15°C over those of PHB. The thermal degradation mechanism of PHB and poly(HB–HV) under nitrogen were investigated with TG–FTIR and Py–GC/MS. The results show that the degradation products of PHB are mainly propene, 2‐butenoic acid, propenyl‐2‐butenoate and butyric‐2‐butenoate; whereas, those of poly(HB–HV) are mainly propene, 2‐butenoic acid, 2‐pentenoic acid, propenyl‐2‐butenoate, propenyl‐2‐pentenoate, butyric‐2‐butenoate, pentanoic‐2‐pentenoate, and CO₂. The degradation is probably initiated from the chain scission of the ester linkage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1530–1536, 2003     

Promoted Fe2O3‐Al2O3‐CuO Chromium‐Free Catalysts for High‐Temperature Water‐Gas Shift Reaction

Promoted Fe₂O₃‐Al₂O₃‐CuO (FAC) chromium‐free catalysts were prepared for high‐temperature water‐gas shift reactions and characterized by X‐ray diffraction (XRD), Brunauer‐Emmett‐Teller method (BET), temperature‐programmed reduction (TPR), and transmission electron microscopy (TEM) techniques. The catalytic results revealed that among the investigated promoted catalysts with Ce, La, Zn, Y, and Mn as promoters, the Mn‐promoted sample showed higher activity compared to the other promoted catalysts. Increasing the Mn content improved the surface area and catalytic activity. The FAC catalyst promoted with a high Mn content exhibited maximum activity and relatively high stability in high‐temperature water‐gas shift reaction.     

Catalytic Hydrocracking of a Bitumen‐Derived Asphaltene over NiMo/γ‐Al2O3 at Various Temperatures

Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al₂O₃ was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage.     

Co–Pd/γ‐Al2O3 catalyst for heavy oil upgrading: Desorption kinetics,reducibility and catalytic activity

The influence of Pd on a Co–Pd/γ‐Al₂O₃ heavy oil upgrading catalyst is investigated using different physicochemical and reactive Characterization techniques. Nitrogen adsorption isotherm analysis shows that the specific surface area and porosity of the support alumina is significantly decreased due to the blockage of the pores by the loaded cobalt species. The estimated activation energy of NH₃ desorption is found to be less for Co–Pd/γ‐Al₂O₃ sample, which confirms improved acidity due to Pd. TPR experiments show that the reducibility of the catalyst is significantly improved with the presence of Pd. Higher metal dispersion and hydrogen spillover effects are the main reasons for the enhanced reducibility of the Pd promoted catalyst as revealed by the H₂‐pulse chemisorptions study. When evaluated using VGO as feed stock, the Co–Pd/γ‐Al₂O₃ displayed superiority both in hydrodesulphurisation (HDS) and hydrocracking (HC) activities as compared to the unpromoted Co/γ‐Al₂O₃ catalyst. The coke deposition on the spent catalyst is also found to be low due to the Pd promotional effects. This is an encouraging result, given that higher hydrogenation activity of the catalyst can be achieved without compromising the cracking activity and sustained activity of the catalyst.     

Catalytic activity of Pt‐Re‐Pb/Al2O3 naphtha reforming catalysts

BACKGROUND: The main purpose of the naphtha reforming process is to obtain high octane naphtha, aromatic compounds and hydrogen. The catalysts are bifunctional in nature, having both acid and metal sites. The metal function is supplied by metal particles (Pt with other promoters like Re, Ge, Sn, etc.) deposited on the support. The influence of the addition of Pb to Pt‐Re/Al₂O₃ naphtha reforming catalysts was studied in this work. The catalysts were prepared by co‐impregnation and they were characterized by means of temperature programmed reduction, thermal programmed desorption of pyridine and several test reactions such as cyclohexane dehydrogenation, cyclopentane hydrogenolysis and n‐heptane reforming. RESULTS: It was found that Pb interacts strongly with the (Pt‐Re) active phase producing decay in the metal function activity. Hydrogenolysis is more affected than dehydrogenation. Part of the Pb is deposited over the support decreasing the acidity and the strength of the most acidic sites. CONCLUSION: The n‐heptane reforming reaction shows that Pb modifies the stability and selectivity of the Pt‐Re catalysts. Small Pb additions increase the stability and greatly improve the selectivity to C₇ isomers and aromatics while they decrease the formation of low value products such as methane and gases. Copyright © 2011 Society of Chemical Industry     

Influence of Parameters on Glycerol Hydrogenolysis over a Cu/Al2O3 Catalyst

The influence of technological parameters like hydrogen pressure, temperature, glycerol concentration in aqueous solution, amount of catalyst, stirring speed, and reaction time on glycerol hydrogenolysis to 1,2‐propanediol over a Cu/Al₂O₃ catalyst prepared by coprecipitation was investigated. Functions describing the process were glycerol conversion as well as selectivity to 1,2‐propanediol and to by‐products in the liquid and gas phase. The structure and properties of synthesized Cu/Al₂O₃ were characterized by X‐ray diffraction, energy dispersive X‐ray microanalysis, BET surface area, average pore volume, and pore diameter. Catalyst recycle studies were also performed.     

Structural elucidation and iron oxidation states in situ formed β‐Ca3(PO4)2/α‐Fe2O3 composites

A detailed structural analysis on the in situ synthesized β‐Ca₃(PO₄)₂/α‐Fe₂O₃ composites is demonstrated. Compositional ratios, the influence and occupancy of iron at the β‐Ca₃(PO₄)₂ lattice, oxidation state of iron in the composites are derived from analytical techniques involving XRD, FT‐IR, Raman, refinement of the powder X‐ray diffraction and X‐ray photoelectron spectroscopy. Iron exists in the Fe³⁺ state throughout the investigated systems and favors its occupancy at the Ca²⁺(5) site of β‐Ca₃(PO₄)₂ until critical limit, and thereafter crystallizes as α‐Fe₂O₃ at ambient conditions. Fe³⁺ occupancy at the β‐Ca₃(PO₄)₂ lattice yields a Ca₉Fe(PO₄)₇ structure that is isostructural with its counterpart. A strong rise in the soft ferromagnetic behavior of β‐Ca₃(PO₄)₂/α‐Fe₂O₃ composites is obvious that depends on the content of α‐Fe₂O₃ in the composites. Overall, the diverse level of iron inclusions at the calcium phosphate system with a Ca/P ratio of 1.5 yields a structurally stable β‐Ca₃(PO₄)₂/α‐Fe₂O₃ composites with assorted compositional ratios.     

Catalytic partial oxidation of CH4 over bimetallic Ni‐Re/Al2O3: Kinetic determination for application in microreactor

The activity of a novel Ni‐Re/Al₂O₃ catalyst toward partial oxidation of methane was investigated in comparison with that of a precious‐metal Rh/Al₂O₃ catalyst. Reactions involving CH₄/O₂/Ar, CH₄/H₂O/Ar, CH₄/CO₂/Ar, CO/O₂/Ar, and H₂/O₂/Ar were performed to determine the kinetic expressions based on indirect partial oxidation scheme. A mathematical model comprising of Ergun equation as well as mass and energy balances with lumped indirect partial oxidation network was applied to obtain the kinetic parameters and then used to predict the reactant and product concentrations as well as temperature profiles within a fixed‐bed microreactor. H₂ and CO production as well as H₂/CO₂ and CO/CO₂ ratios from the reaction over Ni‐Re/Al₂O₃ catalyst were higher than those over Rh/Al₂O₃ catalyst. Simulation revealed that much smoother temperature profiles along the microreactor length were obtained when using Ni‐Re/Al₂O₃ catalyst. Steep hot‐spot temperature gradients, particularly at the entrance of the reactor, were, conversely, noted when using Rh/Al₂O₃ catalyst. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1691–1701, 2018     

YCrO3/Al2O3 Core‐Shell Design: The Effect of the Nanometric Al2O3‐Shell on Dielectric Properties

We report a novel strategy to improve the dielectric properties of the biferroic YCrO₃ ceramic compound through interface conduction control by means of an insulating Al₂O₃ using a core‐shell design. The YCrO₃ particles were covered with several layers of insulating Al₂O₃ using the atomic layer deposition technique to produce the core‐shell structure. TEM images reveal homogeneous and well‐defined Al₂O₃ coatings of ~8, ~60, and ~130 nm thickness. XRD shows the Al₂O₃‐shell to be amorphous. The dielectric characteristics of the sintered nano‐composite were investigated in the 100 Hz–1 MHz frequency range and temperature between 300 and 580 K. As the Al₂O₃‐shell thickness covering the YCrO₃ particles is increased, a decrease of the dielectric permittivity, loss tangent and AC conductivity values was found in the whole range of temperatures and frequencies. Furthermore, the rounded hysteresis loop, typical of conductive ceramic is restored as the insulating Al₂O₃ layer becomes thicker. This behavior is explained because the insulating Al₂O₃‐shell acts as internal barrier layer localizing the surface charges on the sintered grain boundaries. This fact was confirmed by Electron Beam Induced Current technique where a clear contrast at the grain boundaries confirms the charge localization at the YCrO₃/Al₂O₃ interface. These results also reveal that the Al₂O₃‐shell induces another conductive mechanism when the insulating Al₂O₃ layer becomes thicker. Nonetheless, this new strategy is an effective approach to suppress the parasitic conductivity in polycrystalline multiferroic ceramics and increasing thus the multifuncionality.     

Characterization of the effects of β‐carotene on the thermal oxidation of triacylglycerols using HPLC‐ESI‐MS

RP HPLC method coupled to ESI‐MS was used for the analysis and characterization of the oxidation of model triacylglycerols (TAGs) in presence of β‐carotene. β‐Carotene was added to the TAGs and oxidized in the Rancimat at 110°C. The samples were separated isocratically using a mixture of isopropanol with methanol and a Phenomenex C18 column. β‐Carotene degradation was measured using high performance TLC. We found that β‐carotene plays an important role during the thermal degradation of high oleic acid model TAGs. Half of the β‐carotene was degraded before 3 h of thermal treatment. β‐Carotene significantly increases the peroxide value of the TAGs after the third hour, suggesting a pro‐oxidant action. However, different TAGs show different activity toward thermal treatment and β‐carotene. The LLL was found to be less stable, OLL and OLO were stable till 10 and 12 h respectively, while POO, OOO, and OSO were the stable TAGs till 14 h. In TAGs, replacing linoleic acid by oleic acid, the stability of the corresponding TAG was found to increase by 2 h. A new class of oxidized TAGs was reported for the first time, together with previously reported species. The proposed mechanism of formation and identification of the newly identified species have been explained. Among the oxidized species of TAGs, mono‐hydroperoxides, bis‐hydroperoxides, epoxy‐epidioxides, and epoxides were the major compounds identified.