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To experimentally study the effect of supercritical fluid on product desorption, methanol synthesis from CO/CO 2 /H 2 over the Cu/ZnO/Al 2 O 3 catalyst was conducted in the solvents of liquid paraffin, supercritical n -hexane, and their mixture. For the catalyst size of 0.15 mm at which the internal mass transfer resistance was negligible, methanol yields of 10% in n -paraffin and 18% in supercritical n -hexane were obtained respectively. From the conversion rates of CO 2 at different n -hexane pressures, the resistance ratio of CO 2 hydrogenation to methanol desorption was obtained to vary from 1:2.85 to 1:0.75 when n -hexane partial pressure was increased from 0 to 4.0 MPa. Furthermore, the resistance ratio of the consecutive steps of water–gas shift reaction (WGSR), CO 2 hydrogenation and methanol desorption were then evaluated with respect to CO as the reactant. It shows the resistance ratio of the three steps varies from 0.77:1:2.82 to 0.75:1:0.75 when n -hexane partial pressure was increased from 0 to 4.0 MPa. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two-bubble class model was employed for the gas–liquid mass transfer. [•] Axial dispersions of liquid and solid phases are incorporated in above model. [•] Bench-scale experiment was carried out in a 2L stainless steel tube of 2m long. [•] Scale-up simulations at a capacity of 1.0Mt/a for VR processing were conducted. [•] Due to the non-uniform distribution of catalyst, axial dispersion model is required. [ABSTRACT FROM AUTHOR]

Abstract: Hydrodynamics experiments with respect to supercritical and subcritical fluids were conducted in a laboratory-scale trickle bed reactor filled with relatively small particles of 0.67–1.32mm in diameter. Residence time distribution was measured with tracer injection, and the results indicated that the supercritical fluids (SCF) have non-liquid-like features. From the pressure drop fluctuations, the pulsing flow was observed with the increase of the supercritical fluid mass flux; clearly, it shows that SCFs possess liquid-like property. Based on the empirical relationship proposed by Al-Naimi et al. (2011), the experimental data for subcritical fluids could be well correlated, which results in a new correlation in the predication of the pressure drop for fluids at subcritical conditions. [Copyright &y& Elsevier]

Abstract: To evaluate the pore network effect due to variation in catalyst size, adsorption/desorption isotherms of N2 at 77.3K were measured for γ-Al2O3 particles of 4.0, 1.0, 0.5 and 0.04mm in diameter with ASAP 2020 by Micromeritics. It shows the desorption knee is obvious for the 4.0mm particle, while it is not found for the others. Nevertheless, the loops of isotherm hysteresis are decreasing when the particle size is reduced from 1.0 to 0.04mm. Under elevated temperatures with benzene hydrogenation as the working system, it shows the hysteresis in adsorption and reaction rate are remarkable for the 2.0 and 4.0mm particles, but is much less evident when the particle size is reduced to 1.0 and 0.5mm. With the increase of reaction temperature, the hysteresis loop tends to move to the region of high relative vapor pressures, due to the unstable vapor condensation condition in small pores. To inspect how the reaction rate is affected by the variation of catalyst condition, the internal wetting fraction and the internal effectiveness factor are measured and evaluated over a wide vapor pressure range, and an almost linear relationship is found between them. It shows the effective diffusivity of hydrogen under full vapor condensation in the catalyst is about 13 times that filled with bulk liquid, which suggests the catalyst pore can be considered being filled with vapor–liquid mixture rather than with bulk liquid. [Copyright &y& Elsevier]

In reduction of liquid backmixing in bubble columns,Wu et al.[Wu, Y; Cheng, Z. M.; Huang, Z. B. Backmixing reduction of a bubblecolumn by interruption of the global liquid circulation. Ind.Eng. Chem. Res.2009, 48, 6558–6563]have shown that the backmixing could be substantially reduced by interruptingthe global liquid circulation using four identical short Venturi throats(SVTs). Considering the advantages of such structures, it is necessaryto further investigate the backmixing characteristics of a bubblecolumn with SVTs. In the present work, a multipoint tracer injectionand detection device was employed to enhance the insight into whereand how the liquid tracer was backmixed in different stages of a 50-cmdiameter column. Tracer response profiles were measured to track theliquid backmixing trajectory in different stages at various operatingconditions. The results showed that the backmixing of the column wassensitive to the throat diameter of SVTs. Based on the observed physicalphenomena, a tanks-in-series with backflow (TISB) model was adoptedto interpret the tracer experiment data, which shows an excellentagreement between the prediction and experimental measurements. [ABSTRACT FROM AUTHOR]

To experimentally verify the existence of reaction rate hysteresis in the gas phase operation due to capillary condensation, benzene hydrogenation was carried out in a fixed bed under isothermal condition. Through changing the flow rate of benzene and cyclohexane mixture in a sequence from low to high and then vice versa, a group of distinctive conversion profiles was obtained. By plotting the reaction rate against the relative vapor pressure, hysteresis loops in reaction rate are confirmed to exist. It was observed the reaction rate kept nearly constant in the region of p/p0 0.8. In providing an intrinsic understanding on the influence of vapor condensation on the reaction rate of a partially wetted catalyst, the reaction rate and internal effectiveness factor are plotted against the catalyst wetting fraction, from which a new correlation between the overall reaction rate and catalyst wetting fraction was proposed. [ABSTRACT FROM AUTHOR]

A two-stage reactor composed of a slurry bubble column and a fixed bed was proposed. The slurry column, installed with a radio frequency conductance liquid level controller, was considered not only as a preliminary reactor for the vaporization of the liquid reactants, but also as a protector to prevent liquid flooding in the fixed bed. Preliminary experiments were carried out to investigate the effects of different operating factors on the reactor performance, and the results showed that even under the optimal condition the benzene concentration should be kept at a low level of 21.9% to avoid high temperature rise. Therefore, side stream injection of cyclohexane into the fixed bed was proposed, and benzene conversion of 99.82% was reached even at a much higher concentration of 32.8%. To verify whether capillary condensation inside the catalyst particle in the fixed bed would exist in the presence of coolant injection, a criterion was proposed which is based on the understanding that once vapor condensation is occurring it will lead to multiplicity in reaction rate, which will consequently result in hysteresis in temperature profile under adiabatic condition. [ABSTRACT FROM AUTHOR]

Abstract: Citric acid complexation under mild condition was proposed to prepare monophasic and well crystallized Mg3(VO4)2 particle to be used as an active catalyst for the oxidative dehydrogenation of cyclohexane to cyclohexene. The catalyst prepared above was characterized by N2-physisorption, X-ray diffraction, scanning electron microscopy, and thermal gravimetric analysis. The characterization results displayed that the Mg3(VO4)2 particle was typically 100–160 nm and the specific surface area was 12.0–26.7 m2/g. Moreover, it showed that the purity and the structure of the catalyst were principally subjected to the calcination temperature and the amount of citric acid used in the sol–gel procedure. The Mg3(VO4)2 catalyst calcined at 823 K for 6 h with a molar ratio of (Mg+V):citric acid=1:1.2 exhibited the best catalytic performance with an excellent thermal stability. [Copyright &y& Elsevier]

Abstract: The work reported in this paper is aimed at exploring the feasibility of immobilizing alkali lipase from Penicillium expansum on a bimodal ceramic foam, which has both macro- and micro-pore structures. After being chemically modified with a silane coupling agent, the ceramic foam was used as a support for lipase immobilization. To determine the preferable immobilization conditions, the effects of the amount of enzyme for loading, immobilization time, temperature, and pH on enzyme activity were investigated. The results showed that the chemically modified ceramic foam has a high loading capacity and a strong binding ability for the lipase. Thanks to the low internal mass transfer resistance, the ceramic foam has greatly enhanced the rate of immobilization. As a comparison, the immobilized-lipase activity was much higher than that on many frequently used porous materials like diatomite, alumina and activated carbon. [Copyright &y& Elsevier]

Abstract: With the view of increasing the understanding to the anti-scaling mechanism in the membrane process, zeta potential on the anti-scalant (Calgon and PAA) modified sub-micro calcite surface was measured and was further characterized with a molecular simulation. Experimental results show that the original positively charged calcite in an aqueous solution is reversed to be negatively charged by introducing anti-scalants at a dosage of ppm level. On the basis of theoretical calculation, the observed reversal is resulted from the statistically predominant orientation of negative potential-determining groups in the adsorbed anti-scalant molecules, i.e. Pe:glyph name="dbnd" />O, stretching against the calcite surface. A negative zeta potential prevailing on the calcite surface can effectively prevent the calcite from precipitating on the membrane surface. In the presence of anti-scalants, zeta potential on the sub-micro calcite surface is a sensitive function of calcite content, anti-scalant concentration, salt concentration, and pH of the suspension. [Copyright &y& Elsevier]

Abstract: In this work, the denitrogenation of hydrocarbons under supercritical water oxidation environment was investigated in a rotated bomb reactor at 623–723K and 25–35MPa over sulfided NiMo catalyst. Quinoline was used as a model nitrogen-containing compound. A high reduction of total nitrogen up to about 85% was obtained. The denitrogenation pathway is composed of two consecutive steps: in situ H2 generation and the hydrogenation of quinoline. The hydrogenation mechanism of quinoline varies with reaction temperature because of the participation of supercritical water in HDN step. The strong adsorption of quinoline and its hydrogenation intermediates on catalyst surface has an adverse influence on total nitrogen reduction rate. [Copyright &y& Elsevier]

Abstract: Catalytic desulfurization of a model sulfur-containing compound benzothiophene (BT) through partial oxidation in supercritical water (SCW) was investigated in a bomb reactor at 623–723K and 30–40MPa over sulfided CoMo/γ-Al2O3. Vacuum residuum was used to confirm the desulfurization rate and efficiency, and the desulfurization mechanism of vacuum residuum was determined by the pyrolysis temperature (T R) of the vacuum residuum (VR). For T > T R, obvious reduction of sulfides up to 67% was obtained. The thermodynamic equilibrium of in situ H2 generation was a controlling factor of the desulfurization pathway. [Copyright &y& Elsevier]

Abstract: A novel multiphase fixed-bed reactor with continuous phase transition for benzene hydrogenation to cyclohexane has been presented by Cheng et al. (A.I.Ch.E. J. 47 (2001a) 1185; Chem. Eng. Sci. 56 (2001b) 6025; 57 (2002) 3407; A.I.Ch.E. J. 49 (2003) 225) which makes use of evaporation of volatile components to remove the reaction heat. This paper investigates issues related to the numerical simulation of the model for this novel fixed-bed reactor. The reactor is supposed to be divided into two parts subject to the phase transition point on the bed level, that is, the liquid-contacted zone at the lower part and the gas-contacted zone at the upper part. A steady-state mathematical model for the reactor is developed. All external mass and heat transfer resistances can be neglected in the case investigated, as well as temperature differences in the particles. The effects of feed inlet temperature, inlet benzene concentration, gas flow rate and liquid flow rate on the reactor performance are theoretically studied. Reliability of the model is verified by bench-scale experiments. The results show that dryout phenomena will occur in the reactor both on the bed-scale and on the pellet-scale under certain conditions. [Copyright &y& Elsevier]

Abstract: A two-stage concurrently and countercurrently operated fixed-bed reactors were investigated to remove sulpfur and aromatics in producing ultra-clean diesel fuel. Under similar operating conditions, the sulfur concentration in the produced oil through countercurrent operation is much less than under concurrent flow. In a typical run with countercurrent flow at 6.0MPa and 360°C, the sulpfur content could be removed from 13,841 to with nitrogen from 457 to and the total aromatics from 41.4% to 26%. One-dimensional heterogeneous model was established to simulate the distribution of all the components involved along the reactor length in the gas and liquid phases, which revealed that the low H2S concentration at the reactor exit region under countercurrent flow is critical to the ultra low sulphur extent in the produced oil. [Copyright &y& Elsevier]

The effect of partial internal wetting of catalyst pellets on apparent reaction kinetics at elevated temperatures and pressures is investigated experimentally and by modeling for benzene hydrogenation. A new method that combines adsorption and chemical reaction is introduced to study the kinetics influenced by capillary condensation of reagents at steady-state conditions. It is shown that the extent of liquid filling in the pellet interior has a critical effect on the global kinetics, and the current state of the catalyst depends on the history. Under certain conditions two steady states of the effectiveness factor exist. Moreover, either a decrease in temperature or increase in total pressure can increase the effectiveness factor. The model exhibits good agreement with experimental results. [Copyright &y& Elsevier]

[Display omitted] • The annular swirling flow reactor excels in liquid–liquid mixing. • Conical structure effectively inhibits attenuation of swirling flow intensity. • Main mass transfer region of the reactor is near the central conical wall. • The swirling flow reactor exhibits superior crystal preparation capability. • In reaction crystallization, the swirling flow reactor shows unique potential. This study investigates the performance of an annular conical swirling flow reactor in liquid–liquid reactions for the preparation of inorganic salt particles. Utilizing Particle Image Velocimetry (PIV) measurements and Computational Fluid Dynamics (CFD) simulations, it was observed that the conical design effectively inhibited the attenuation of swirling flow intensity along the axial direction, with the primary mass transfer region close to the central conical wall. In comparison to a stirred reactor, calcium carbonate particles synthesized in the swirling flow reactor exhibited more uniform morphology, smoother and defect-free surface. Notably, the average particle size remained consistently within 5–6 μm (excluding the 0.3 M feedstock), whereas stirring led to particles with an average size ranging from 8-11 μm. Analysis of the residence time distribution curve revealed minimal back mixing in the swirling flow reactor, ensuring nearly equal growth time for salt particles, thus yielding particles with a uniform size distribution. As a result, the swirling flow reactor presents compelling prospects for applications in reactive crystallization. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics simulation and Density Functional Theory were used to investigate the adsorption of two kinds of anti-scalant, ethane diphosphonic acid (EDPA) and polyether polyamino methylene phosphonate (PAPEMP), on the calcite (104) surface in order to increase the level of understanding of the anti-scaling mechanism in membrane processes for water desalination. Calculation results show that the performance of an anti-scalant is mainly determined by the negative electrostatic potential presented on the anti-scalant modified scale surface. A negative electrostatic potential on the scale surface can prevent not only the agglomeration of scale nuclei in the concentrate but also the precipitation of scale nuclei on the membrane surface. Phosphonate groups in 1,1-EDPA are bifunctional since they simultaneously satisfy the requirements for the electrostatic potential distribution and for the adsorption stability on the scale surface. As concerns PAPEMP, the above requirements are fulfilled respectively by different functional groups, i.e. ether groups and phosphonate groups. To simplify the role of functional groups in the anti-scaling mechanism means that the performance of an anti-scalant can be optimized by the combination of specific functional groups; furthermore, these functional groups can also be adjusted with respect to different scale surfaces. [Copyright &y& Elsevier]

Abstract: For the sake of improving the performance of Ru-based catalyst used in partial hydrogenation of benzene to cyclohexene, the effect of Zn2+/Zn layer on the adsorption and dissociation of H2 on Ru (0001) surface was investigated by applying density function theory (DFT) calculations. Calculation results show that the dissociation of H2 occurs only after its being chemisorbed horizontally at atop site. Because of the influence of Zn2+ on the electron delocalization between molecular orbit of H2 and valence orbits of atop Ru atom, a remarkable increase in the H2 dissociation barrier is noticed, which results in zones of sparse chemisorbed H around Zn2+. Adsorbed Zn2+ can be reduced by chemisorbed H, and the H2 dissociation kinetics varies little in the presence of Zn atoms at adjacent sites. Split zones of chemisorbed H are formed at a high coverage of Zn layer. The consecutive or synchronous hydrogenation of benzene is disturbed when benzene is adsorbed in zones of sparse chemisorbed H or split zones of chemisorbed H. It is therefore deducted that a high coverage layer of some transition metal atoms on catalyst surface should be helpful for maintaining the hydrogenation activity of the catalyst and improving the cyclohexene yield. [Copyright &y& Elsevier]

Graphical abstract By the differences in heavy oil composition and thermodynamic state of water applied, the oil-in-water emulsion structure of heavy oil/SCW systems may transit to the condensed emulsion or pseudo single-phase structure, determining their feasible application in upgrading of heavy oil. Highlights • MD simulation on dissolution of PAHs or PAH mixtures in sub-CW/SCW was applied. • Dissolution of heavy PAHs in sub-CW/SCW is sensitive to thermodynamic state of water. • Preferential dissolution of light PAHs occurs during dissolution of PAH mixtures. • Electrostatic interaction promotes the dissolution of PAHs in sub-CW/SCW. • Heavy oil/SCW could exist in condensed emulsion or pseudo single-phase structure. Abstract To get a better understanding of the upgrading of heavy oil under severe hydrothermal environment, a molecular dynamics simulation on the dissolution of oil droplets containing polycyclic aromatic hydrocarbons (PAHs) or PAH mixtures in subcritical or supercritical water (sub-CW/SCW) was applied. Being the representative of light PAHs, naphthalene dissolves readily into sub-CW/SCW. The dissolution of heavy PAHs, like benzo[α]pyrene and benzo[ghi]perylene however is sensitive to the thermodynamic state of water. During the dissolution of PAH mixtures, a preferential dissolution of light PAHs into the water phase occurs, leaving heavy PAHs concentrated in the oil droplets. With the simultaneous increase in water density and temperature, the miscibility of PAHs with sub-CW/SCW is improved by the enhanced attractive electrostatic interaction between PAHs and hydrothermal environment and the weakened interaction between PAHs. By the differences in heavy oil composition and the thermodynamic state of water, the upgrading of heavy oil in sub-CW/SCW could be run in the condensed emulsion or pseudo single-phase structure. [ABSTRACT FROM AUTHOR]

To improve the understanding of the condensation of asphaltenes in supercritical water (SCW), the solvation of asphaltenes under SCW environments was investigated with molecular dynamics simulation. The simulation results indicate that the repulsive van der Waals interaction has a primary influence on the nature and the magnitude of the interaction between asphaltenes and SCW. A cavity short-range solvent structure surrounding asphaltenes thus is formed, and the solvation free energy ( G sol ) of asphaltenes in SCW has a positive sign in most cases. The scale of cavities and the value of G sol both are determined mainly by the bulk density of water. By the repulsive asphaltenes/SCW interaction and the attractive π–π aromatic interaction, the aggregation of asphaltenes in SCW occurs spontaneously. The asphaltene clusters formed, containing asphaltene monomers and nanoaggregates, present a coke-like supramolecular structure. Benefiting from excellent diffusivity in SCW, the aggregation of asphaltenes in SCW can be accomplished rapidly. [ABSTRACT FROM AUTHOR]

A stochastic model was developed to describe the liquid radial dispersion in a trickle-bed reactor, which has conventionally been modeled by the effective diffusion model. To establish the stochastic model, the column was divided into some layers of particles in the axial direction and several annulus rings in each layer in the radial direction. The liquid spreading was regarded as a fluid transport process and the matrix of transfer probability was derived based on the coordinates of the particle network in the cross-section of the column. With this transfer probability matrix and the initial liquid distribution, the liquid distribution in the downstream was predicted. In order to evaluate the model parameters, experimental data of the liquid dispersion were obtained from electrical capacitance tomography images and tracer injection. Good agreement was obtained between the stochastic model and the experimental liquid distribution data. [ABSTRACT FROM AUTHOR]

Abstract: At 693K and water density of 0.30g/cm3, the co-pyrolysis of heavy oil and low density polyethylene (LDPE) in the presence of supercritical water (SCW) was investigated with the emphasis on the coking mechanism involved. The co-pyrolysis in SCW was found to have the significant advantages of the decreasing yield of coke and the increasing yield of aromatics over the pyrolysis of heavy oil alone in SCW. With the increase in the loading of LDPE, the suppression of condensation in co-pyrolysis is gradually intensified, suggesting the essential role of LDPE as an external H-source in co-pyrolysis. Only in the continuous SCW phase can the H-donation between the pyrolysis networks of heavy oil and LDPE be effectively accomplished, by which the condensation of light oil fractions to heavy oil fractions and the deep condensation of asphaltenes to coke are partly suppressed. [Copyright &y& Elsevier]

Abstract: The initiated pyrolysis of heavy oil in the presence of near-critical water (near-CW) was investigated with density functional theory (DFT) calculation and experimental characterization. Theoretical calculation indicated the thermodynamic feasibility of forming hydrocarbon radicals in heavy oil with the aid of appropriate radical initiators. By introducing ditertbutyl peroxide (DTBP) into heavy oil, the H-abstraction of Hβ atoms distributed mainly in the fractions of saturates, resins, and asphaltenes occurs, forming hydrocarbon radicals located on aliphatic chains with priority. At the temperature of 653K and water density of 0.30g/cm3, it was experimentally confirmed that the introduced DTBP was capable of initiating the pyrolysis of heavy oil. After 15min''s reaction, the pyrolysis products centered toward the fraction of aromatics whose weight proportion in the liquid product increased drastically by ca. 25.0wt.%. Meanwhile, only a negligible coke yield of 0.5wt.% was collected. [Copyright &y& Elsevier]

Abstract: At the temperature of 693K and water densities from 0.10 to 0.30g/cm3, co-pyrolysis of residual oil and polyethylene in sub- and supercritical water (sub-CW and SCW) was experimentally investigated. With the increase in water density, the phase structure of the co-pyrolysis system may evolve from a liquid/liquid/solid three-phase structure to a liquid/solid two-phase one. By co-pyrolysis of polyethylene with residual oil, H-rich paraffins, the main pyrolysis product of polyethylene, are released continuously into the reaction system. At higher water densities with the favorable liquid/solid two-phase structure, the contact of aromatic radicals from the pyrolysis of residual oil and paraffins from that of polyethylene is promoted, ensuring the coupling between pyrolysis networks of residual oil and polyethylene. Consequently, dealkylation of aromatic radicals may follow the desired mechanism by which the production of coke-inducing components is effectively depressed. A significantly reduced coke yield is observed in the co-pyrolysis of residual oil and polyethylene in sub-CW and SCW. [Copyright &y& Elsevier]

Abstract: To increase the understanding of the reaction behavior of heavy hydrocarbons in the presence of sub- and supercritical water, upgrading of residual oil was applied in a batch reactor at temperatures of 653 to 713K and water densities of 0.05 to 0.20g/cm3. It is confirmed that upgrading of residual oil in sub- and supercritical water is still dominated by the free radical mechanism based thermal cracking. The ion mechanism based hydrolysis only has an extremely limited influence on the upgrading performance. With the increase in water density, the upgrading system may evolve from a partially miscible two-phase structure to a pseudo single-phase structure in which asphaltenes are highly dispersed in the continuous water phase. Prompt diffusion of aromatic radicals from asphaltenes into the water phase both depresses the coke formation and improves the liquid product distribution. [Copyright &y& Elsevier]

Abstract: Solvation of methyl radicals in subcritical and supercritical water was investigated with the ab initio MD simulation to increase the understanding of the thermal cracking of hydrocarbons under the severe hydrothermal environments. The calculation results show that water clusters around the radical could be formed with the following prerequisites: the bulk density of water is close to liquid phase, and the state point of water on its phase diagram is far away from the critical point and from the vapor–liquid equilibrium boundary. The occurrence of water clusters superimposes a negative influence on the originally depressed diffusivity of the radical under the dense hydrothermal environments, and the interference from the immediately adjacent water molecules with the frontier orbitals of the radical results in randomly reduced activity of the radical. Regardless of whether there are water clusters around the radical or not, in subcritical and supercritical water the bimolecular reactions participating via hydrocarbon radicals should be partially suppressed by the reduced diffusivity and lower activity of the radical. [Copyright &y& Elsevier]

Abstract: WO x /ZrO2 catalyzed hydration of cyclohexene in sub-critical water was experimentally investigated. The migration of reaction zone into sub-critical water makes it possible to run the hydration in a single liquid phase, and the reaction is free from the limitation of liquid–liquid phase mass transfer to hydration kinetics. The severe hydrothermal environments favor the transformation of surface active sites on WO x –ZrO2 catalysts to Brønsted acid centers of stronger acidity, which are highly effective for the hydration of cyclohexene to the desired product cyclohexanol. [Copyright &y& Elsevier]

Abstract: In this work, hydrophilic property of Ru (0001) with and without H adatoms was theoretically studied to increase the understanding of the partial hydrogenation of benzene to cyclohexene over ruthenium catalysts. Density functional theory based calculations suggest that formation of hydrogen bonding among the adsorbed H2O molecules results in a weakened interaction between the water adlayer and Ru (0001), while the calculated heat of adsorption containing the contribution of hydrogen bonding is no longer suitable for evaluating the hydrophilic property of the metal surface. The presence of H adatoms exerts an electrostatic repulsion on the adsorbed H2O molecules; thereby the latter can be in the state of chemisorption or physisorption on the Ru metal depending on the number of immediately adjacent H adatoms and on the relative distance to the H adatoms. By tuning the coverage of H adatoms, the surface hydrophilic/hydrophobic balance of the Ru metal can be effectively adjusted, which provides an approach to improve the selectivity to cyclohexene in the partial hydrogenation of benzene. [Copyright &y& Elsevier]

Abstract: From the adsorption point of view, partial hydrogenation of benzene to cyclohexene over the metallic Zn modified Ru-based catalyst was experimentally and theoretically investigated. A decreased hydrogenation activity but increased selectivity to cyclohexene over the prepared Ru-Zn/ZrO2 catalyst was observed in the partial hydrogenation of benzene. Theoretical calculations suggest that the above phenomena are mainly resulted from the depression of the chemisorption of benzene and cyclohexene on the modified catalyst, especially for the latter. Undesired deep hydrogenation from cyclohexene to cyclohexane in the middle and late reaction stage therefore is effectively retarded, by which an improved cyclohexene yield is guaranteed. An optimal Zn content of 2.72wt.% in the Ru-based catalyst was proposed by both the experiment and calculation for the partial hydrogenation of benzene, and a cyclohexene yield up to 44% was obtained over Ru-Zn/ZrO2 catalyst. [Copyright &y& Elsevier]

Abstract: In this work, the hydrogenation of cyclohexene over Ru–Zn/Ru(0001) surface alloy was investigated by a DFT study so as to improve the understanding of the catalytic mechanism of the partial hydrogenation of benzene to cyclohexene over Ru–Zn alloy catalyst. Calculation results show that the presence of Zn atoms on the surface alloy results in not only a direct decrease in sites for the chemisorption of cyclohexene but also a depressed adsorption capability of the neighboring surface Ru sites. For an adsorbed cyclohexene molecule, whether the subsequent hydrogenation can be readily performed actually is determined by the relative position among the Zn atom, the H atom, and the adsorbed cyclohexene molecule. In most cases, the hydrogenation is forbidden because of the repulsion from Zn atoms to the nearby H atoms. Only in the specific situations in which the H atom participating in the reaction is not immediately close to the Zn atom, can the hydrogenation be accomplished with a relatively lower activation energy compared with the reactions on the Ru(0001) surface. From the perspectives of adsorption and reaction kinetics, Ru-based catalyst modified by metallic Zn is no longer suitable for the hydrogenation of cyclohexene, which is supposed to be crucial to the improvement of cyclohexene yield in the partial hydrogenation of benzene over Ru–Zn alloy catalyst. [Copyright &y& Elsevier]

Abstract: Hierarchically macro–mesoporous titania was synthesized by the simple dropwise addition of tetrabutyl titanate to an ammonia solution in the absence of surfactant molecules, and then calcined at different temperatures. The as-prepared titania was characterized by X-ray diffraction, N2 adsorption–desorption analysis and scanning electron microscopy. The results showed that the hierarchically marcro–mesoporous structure of the titania was well preserved after calcination at 650°C, indicating high thermal stability. The 500°C calcined titania with the hierarchically bimodal pore network was impregnated with 0.5wt.% of palladium and compared with 0.5wt.% Pd/TiO2 catalyst without such macrochannels. The novel macro–mesostructured Pd/TiO2 catalyst exhibited higher catalytic activity for styrene hydrogenation due to the lower diffusion resistance of species inside the catalyst caused by the hierarchically macro–mesoporous bimodal structure. [Copyright &y& Elsevier]