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Methane oxidation using O2 over transition metal oxides often requires severe conditions ( >500 °C) to achieve detectable conversion. In this study, NO was used to transfer oxygen atoms from O2, through the facile gas-phase formation of NO2 at moderate conditions (0.1 MPa and 300–400 °C), to oxidize methane over silica-supported transition metal oxides (VOx, CrOx, MnOx, NbOx, MoOx, and WOx). In situ infrared spectroscopy measurements indicated that the reaction likely proceeded by the formation of surface monodentate nitrate intermediates. These nitrate species were formed by the interaction between adsorbed NO2 and the supported metal oxides. During the reaction, the oxides of vanadium, molybdenum, and tungsten formed formaldehyde and CO2, whereas the oxides of chromium, manganese, and niobium produced only CO2. These results are consistent with the known hydrocarbon oxidation chemistry of the metal oxides. Contact time measurements on VOx/SiO2 indicated that formaldehyde was a primary product and CO2 was the final product; conversely, analogous measurements on MnOx/SiO2 showed that CO2 was the sole product. The formaldehyde production rate on VOx/SiO2, MoOx/SiO2, and WOx/SiO2, based on surface sites measured by high temperature oxygen chemisorption, compared favorably to oxygenate production rates for stronger oxidants (N2O and H2O2) reported in the literature.

The direct partial oxidation of CH4 to dimethyl ether (DME) was achieved with a Pt/Y2O3 catalyst using a mixture of NO and O2. The actual gas composition contained a mixture of NO and NO2, with no decomposition or net consumption of these species. Use of 18O2 confirmed the transfer of labeled oxygen from O2 to CH4, indicating the NO/NO2 mixture worked as a single oxygen atom shuttle.

The direct partial oxidation of CH4 to dimethyl ether (DME) on a Pt/Y2O3 catalyst was studied using a mixture of NO and O2 as the oxidant. The reaction was carried out in a fixed bed reactor at 0.1 MPa and 275–400 °C using 20% CH4, 1% NO, and 1% O2 in inert gas. No methanol was detected in the effluent and a contact time study demonstrated that DME was a primary product. The DME productivities were comparable to the oxygenate (methanol, formaldehyde) productivities obtained with stronger oxidants such as N2O, H2O2, and O3. The presence of Pt and the NO + O2 gas mixture was necessary for DME formation; without NO only CO2 was produced. During the methane partial oxidation reaction NO and NO2 were not reduced to N2, indicating that they worked as a shuttle to transfer oxygen from O2 to CH4. In situ Fourier transform infrared showed the formation of a bridged nitrate species on the Pt/Y2O3 catalyst which was associated with the reaction of CH4. A comprehensive study of this bridged nitrate species indicated they were formed on yttria sites close to Pt and were likely responsible for the formation of DME. The characterization of catalysts using X-ray diffraction showed that the Pt was highly dispersed and CO uptake measurements indicated a particle size of ~3 nm. Analysis by X-ray absorption fine structure measurements showed the presence of Pt oxide with Pt-O and Pt-Pt bonds.

The continuous liquid phase synthesis of nickel phosphide (Ni2P) nanoparticles was studied in a helically coiled tube (HCT) reactor both in single-phase and two-phase slug flows. The reactants were nickel acetylacetonate and tri-n-octylphosphine (TOP) in a 1-octadecane solvent. For the single-phase mode, various parameters such as reaction temperature, residence time, TOP concentration, and P/Ni ratio were studied. It was found that lower temperatures of 320 and 340 °C resulted in the formation of mixed Ni12P5 and Ni2P phases, while a higher temperature of 360 °C gave mostly Ni2P, with particle sizes increasing from 28 to 42 nm. Upon varying the contact time between 88 and 340 s at 360 °C, a likely sequence of reaction involved an amorphous phase that was transformed in parallel to Ni, Ni12P5, and Ni2P. When the flow in the HCT was changed to a two-phase slug flow by using N2 to split the continuous liquid phase into small liquid columns, the product was nearly 100% Ni2P and the particle size was as small as 3–4 nm. This was attributed to the enhanced mass transfer in the small liquid columns of the slug flow that led to higher reaction rates. It is highlighted that the HCT operated in a slug flow is an efficient and continuous method for the fabrication of nanoparticles.

Several Cu/ZnO/Al2O3 catalysts with high Cu and ZnO contents were used to study the influence of solvent polarity on the dehydrogenation and dehydration of isoborneol. The employment of a polar solvent enhanced the activity for the main dehydrogenation reaction, while the use of a non-polar solvent favored the dehydration side-reaction. Different techniques were employed to characterize the fresh, treated, and spent catalysts. X-ray powder diffraction (XRD) showed that the copper was in metallic form and zinc in oxide form, transmission electron microscope (TEM) showed differences in catalyst morphology that depended on the polarity of the solvent used, N2O titration gave the Cu active site density, and temperature-programmed desorption of NH3 (NH3-TPD) provided the acidity of the materials. The characterization results indicated that in non-polar solvents the copper nanoparticles were sintered and this may have been due to the enhanced activity of adventitious water in those solvents or simply because of interactions between the solvents and the copper and zinc oxide components. The sintering resulted in a decrease in the number of active sites and an increase in acidic sites, which enhanced the undesired dehydration reaction. Based on the results of inductively coupled plasma (ICP) and TEM, a model of the catalyst was proposed to illustrate the effect of solvent polarity on the dehydrogenation of isoborneol.

A variety of silica-supported metal oxide catalysts were prepared by the incipient wetness impregnation method and were used for the conversion of dihydroxyacetone to lactic acid. A titanium oxide catalyst with Bronsted acid sites was selective to an intermediate, pyruvaldehyde and a chromium oxide catalyst with Lewis acid sites was selective to lactic acid. The co-impregnation of chromium- and titanium oxides with different ratios accelerated the reaction rate and improved the lactic acid yield up to 80% at 130 °C. Pyridine-adsorbed Fourier-transform infrared spectroscopy indicated that the silica-supported mixed oxides had both Bronsted acid and Lewis acid sites and the trend of the Lewis/Bronsted ratio was close to that of selectivity to lactic acid. Diffuse reflectance UV–vis spectroscopy showed that the silica-supported chromia-titania catalyst composed of isolated Cr and Ti species in tetrahedral coordination. Kinetic analysis revealed that the two critical rate constants, pyruvaldehyde formation and lactic acid formation, for the chromia-titania catalyst were much higher than those of the titania and chromia catalysts.

Hexagonal boron nitride (h-BN) was ball-milled at various rotation speeds (150–600 rpm) using a planetary ball-mill. Ball-milling disrupted the layered structure of the h-BN, resulting in significant increases of surface area. Ball-milling at 400 rpm gave the highest surface area of 412 m2 g−1 while higher rotation speeds decreased the surface areas due to agglomeration. Moreover, ball-milling resulted in the emergence of amino- and hydroxyl groups on the surface which were observed by Fourier transform infrared spectroscopy, and partial oxidation of the surface boron by the formation of B–OH groups was confirmed by X-ray photoelectron spectroscopy. The appearance of trigonal B–O and tetrahedral B–O was observed by boron-11 magic-angle spinning nuclear magnetic resonance spectroscopy. The number of base sites was increased with the increase of rotation speeds of milling, corresponding to the formation of amino groups. The ball-milled h-BN showed catalytic activity for the nitroaldol reaction between nitromethane and benzaldehyde in which the h-BN milled at 400 rpm exhibited the highest reaction rate and turnover frequency. In addition, the ball-milled h-BN could convert glucose with the formation of fructose at 40 °C whereas pristine h-BN showed no activity. The base sites were mainly responsible for the catalytic activity.

Ball-milled hexagonal boron nitride (h-BN) involving oxidized boron on the surface was found to catalyze oxidative dehydrogenation of ethane with high selectivity to ethylene (92–96%) whereas prist...

Hydrothermally stable silica-alumina composite membranes were synthesized through chemical vapor deposition (CVD) of tetraethylorthosilicate (TEOS) and aluminium tri-sec-butoxide precursor at 923 K on porous alumina supports. The membranes showed high hydrogen permselectivity (order of 10−7 mol m−2 s−1 Pa−1) comparable to that of pure silica membranes but with superior hydrothermal stability, and were used in a membrane reactor. The permeation of small gas species (H2, He, Ne) was well explained by a solid-state diffusion mechanism, involving jumps of the permeating species between solubility sites. The permeation mechanism of large gas molecules (CH4, CO2, N2) was explained by the gas translation mechanism involving large pore defects. Steam methane reforming (SMR) on a Ni/MgO-SiO2 catalyst was carried out at 923 K in the membrane reactor and in a conventional packed-bed reactor. The membrane contributed to an increase in the hydrogen production rate by the selective extraction of hydrogen from the reaction zone.

Hydrogenation of furanic compounds is one of the important reactions for upgrading of bio-oils and production of diesel fuels. Platinum catalysts supported on amorphous silica and hexagonal boron nitride (h-BN) were prepared by incipient wetness impregnation and subsequent reduction, and were used for the vapor-phase hydrogenation of 2,5-dimethylfuran in hydrogen at atmospheric pressure and a temperature range of 150–350 °C. For the same amount of Pt loading (1 wt%), the particle size of Pt supported on h-BN was larger than that on silica, resulting in a lower amount of CO chemisorption for Pt/BN than that for Pt/SiO 2 . Using the same amount of active sites, Pt/BN exhibited a 3-fold higher turnover frequency than Pt/SiO 2 for the hydrogenation of 2,5-dimethylfuran whereas both catalysts gave similar product distributions with high selectivity to 2-hexanone at any conversion and low selectivity to n -hexane at high conversion. Contact time studies of 2,5-dimethylfuran hydrogenation on Pt/BN suggested that 2,5-dimethylfuran formed the ring-opening product, 2-hexanone and the ring-saturation product, 2,5-dimethyltetrahydrofuran in parallel, with the rate of the direct furan ring-opening being 9-fold higher than that of the furan ring-saturation.

Catalysts consisting of Ni 2 P placed on low and high surface area siliceous supports, i.e. SiO 2 -L, SiO 2 -H, and Si-MCM-41, were synthesized by TPR (temperature-programmed reduction), and the effect of the sulfur and nitrogen content of the feed on hydrotreating activity was studied. Structural information on the supported Ni 2 P phase after reaction was obtained by XRD (X-ray diffraction) and EXAFS (extended X-ray absorption fine structure) measurements. The catalytic activity in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) was obtained at 573 and 613 K and a pressure of 3.1 MPa in an upflow, liquid-gas-solid bed reactor with a feed consisting of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and quinoline dissolved in tridecane as solvent. Using reference compositions of 4,6-DMDBT at levels of 500 ppm S, dimethyldisulfide (DMDS) at levels of 6000 ppm S, and quinoline at levels of 200 ppm N, the order of activity was Ni 2 P/SiO 2 -L 2 P/SiO 2 -H 2 P/MCM-41, compared on the basis of equal number of sites (230 mmol) placed in the reactor. The Ni 2 P/MCM-41 gave a notably high conversion in HDS of 98% that was substantially above those of a Ni-Mo-S/Al 2 O 3 commercial catalyst which had an HDS conversion of 81%, on a basis of equal quantity of sites (230 mmol) placed in the reactor. The sites were titrated by pulse CO uptakes for the phosphides and by pulse O 2 adsorption at low temperature for the sulfide. Analysis of the spent samples by EXAFS showed that Ni(2) sites of square pyramidal geometry in Ni 2 P are bound to sulfur, with a lower Ni S coordination, as the particle size decreased, and the order in the number of these sites followed the reactivity Ni 2 P/SiO 2 -L 2 P/SiO 2 -H 2 P/MCM-41. It is thus concluded that the active Ni(2) site on the highly dispersed Ni 2 P is much more tolerant to sulfur than the tetrahedral Ni(1) sites also present in the samples.

A hydrogen-selective silica-zirconia composite membrane was prepared on a macroporous alumina support by chemical vapor deposition of tetraethylorthosilicate (TEOS) and zirconium (IV) tert-butoxide (ZTB) at 923 K. The resulting membrane had a high H2 permeance of 3.8×10−7 mol m−2 s−1 Pa−1 with selectivities over CO2, N2 and CH4 of 1100, 1400 and 3700, respectively. Studies of the temperature dependence of the permeance of He, H2, and Ne demonstrated that the permeation mechanism was similar to that of dense silica membranes, involving solid-state diffusion with jumps of the permeating species between solubility sites. Parameters such as the site density, jump distance, and jump frequency were calculated and were physically plausible, and varied in reasonable manner with the mass and size of He, H2, and Ne. An alternative mechanism involving an activated gas translational mechanism was shown to fit the data but to give physically unrealistic parameters. The silica-zirconia membrane showed hydrothermal stability over a limited testing period of 48 h. After exposure to 16 mol% water vapor at 923 K for 48 h, a pure silica membrane showed a 68% decline with a H2 permeance of 4.5×10−8 mol m−2 s−1 Pa−1 and a H2 over N2 selectivity of 800, both of which continued to deteriorate. In comparison, a 10% ZrO2-SiO2 membrane showed a decline of 56% but to a level of 10−7 mol m−2 s−1 Pa−1 with a H2 over N2 selectivity of 5700. Importantly, the deterioration largely stabilized at that permeance level.

Photocatalytic water splitting is an environmentally-friendly method for hydrogen formation, but usually H 2 and O 2 , are produced together, so separation is needed. This paper describes the separation of the gases with supported liquid membranes. The permselective liquids were various perfluorocarbon-based fluids, Dimethyl perfluorosebacate ((CF 2 ) 6 (COOCH 3 ) 2 ), ethyl perfluorononanoate (CF 3 (CF 2 ) 7 COOC 2 H 5 ), perfluoro(perhydrophenanthrene) (C 14 F 24 ) and 1H,1H,2H,2H-perfluorodecyl acrylate (CF 3 (CF 2 ) 7 (CH 2 ) 2 OCOCH=CH 2 ). It was found that the perfluorodecyl acrylate-based liquid membrane showed the highest performance with H 2 permeance of 2.4×10 −9 mol m −2 s −1 Pa −1 (6700 barrers) and a H 2 /O 2 selectivity of 10. The permeance properties of H 2 and O 2 were measured by a time-lag technique and respective diffusivities of 1.1×10 −8 and 6.7×10 −9 m 2 s −1 and solubilities of 2.7×10 −4 and 4.1×10 −5 mol m −3 Pa −1 , were obtained. The lifetime of the membrane was over 48 h, which was much longer than that of other perfluorocarbon-based liquid membranes. The membrane was also stable at humid conditions.

Understanding the reactions of heteroatomic cyclic compounds is essential for developing good catalysts for the upgrading of bio-oils into liquid fuels. The present study presents the reaction network of 2-methyltetrahydrofuran (2-MTHF, C5H10O), a bio-oil model compound, on silica-supported nickel phosphide at 0.1 MPa and 300 °C. Contact time experiments showed that 2-MTHF reacted to first form 1-pentanol and 2-pentanol, then n-pentanal, 2-pentanone, and 1- and 2-pentenes, and finally n-pentane. The observation is consistent with a reaction network in which adsorption of 2-MTHF is followed by rate-determining ring-opening steps on the more hindered side (path I) or the more open side (path II) to first produce adsorbed alcohols. The alcohols then transform into adsorbed aldehyde, ketone, and pentene species which can simply desorb or react to produce the final product n-butane (decarbonylation of adsorbed n-pentanal) or n-pentane (hydrogenation of adsorbed pentenes). Kinetic modeling of the proposed react...

The potential impact of nitrogen and ammonia exposure on hydrogen permeance through thin palladium membranes (1.3 µm to 4.1 µm thick) fabricated by electroless plating was studied. Additionally, a robust approach is introduced to quantify the pressure exponent which accounts for contributions to Knudsen flow through defects present in very thin membranes. In sharp contrast to previously published results, no flux inhibition was observed due to nitrogen or ammonia exposure. Studies included 24 h exposures to both pure gases and equimolar hydrogen/nitrogen or hydrogen/ammonia mixtures at trans-membrane pressures ranging up to 1.0 MPa and temperatures of 598 K to 773 K. One membrane did exhibit significant flux inhibition after helium exposure, but this was attributed to changes in surface microstructure associated with hydrogen departing the lattice. This apparent hydrogen flux inhibition behavior was permanently eliminated by air exposure which roughens the surface, and it is suggested that this surface structure mechanism is a more probable explanation for flux inhibition than adsorption of nitrogen–based species.

As an electrolyte for intermediate-temperature fuel cells (ITFCs), which are operative at 200 °C to 300 °C, a composite electrolyte CsH5(PO4)2/SiP2O7 has been investigated. The CsH5(PO4)2/SiP2O7 composite is reported to exhibit higher conductivity than pure CsH5(PO4)2, possibly by forming a highly-conductive new phase at the interface between CsH5(PO4)2 and SiP2O7. In this study, we have prepared several SiP2O7 matrices of different surface properties, and studied the effect of the surface properties on the total conductivity as well as on the formation mechanism of the interfacial conductive phase. An effective medium approximation method was applied to the measured conductivity to analyze the interfacial conductive phase. Several SiP2O7 matrices of different acid properties and crystalline properties were fabricated, and the conductivity of the CsH5(PO4)2/SiP2O7 composite electrolyte was measured by AC impedance method. The acidity and crystallinity of the SiP2O7 matrices were found to be important properties for the formation of the interfacial conductive phase. The highest conductivity of the interfacial conductive phase was estimated to be 500 mS cm− 1, which is almost three times larger than that of the pure CsH5(PO4)2, 160 mS cm− 1.

Pyrolysis bio-oil is a promising source of liquid fuels, but requires upgrading to remove excess oxygen and produce a satisfactory fuel oil. Nickel phosphide has been shown to be an active composition for hydrodeoxygenation (HDO) of bio-oil model compounds. In this study, nickel phosphide catalysts were used for direct upgrading of an actual pyrolysis bio-oil derived from cedar chips. The activity of Ni2P deposited on an amorphous SiO2 support for HDO was first verified using the model compound, 2-methyltetrahydrofuran (2-MTHF), at the temperature of the pyrolysis oil treatment of 350 °C. The Ni2P/SiO2 catalyst showed high activity for 2-MTHF hydrodeoxygenation under atmospheric pressure hydrogen with low cracking activity. Fast pyrolysis and catalytic upgrading were conducted sequentially using a laboratory-scale, two-stage system consisting of a fluidized bed pyrolyzer and a fluidized bed catalytic reactor both operating at 0.1 MPa, with a hydrogen partial pressure of 0.06 MPa. It was found that the Ni2P/SiO2 catalyst was moderately effective in upgrading the biomass pyrolysis vapors and producing a refined bio-oil with decreased oxygen content. The moderate deoxygenation of the bio-oil was confirmed by elemental analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. Gas chromatography–mass spectrometry (GC–MS) analysis showed that the treated bio-oil mainly consisted of phenolic compounds, and the MS spectra before and after upgrading suggested that reactions including hydrodeoxygenation, hydrogenation, decarbonylation, and hydrolysis occurred during the upgrading. Furthermore, Ni2P supported on ZSM-5 zeolite eliminated oxygen in the bio-oil with smaller reduction in the oil yield than Ni2P supported on SiO2. The deoxygenation activity of the nickel phosphide catalysts was higher than that of conventional catalysts such as Ni/SiO2, Pd/C and an FCC-catalyst.

A series of nickel phosphide catalysts supported on ultrastable Y zeolites USY (Si/Al = 40) with microporous/mesoporous structure were prepared by impregnation and temperature-programmed reduction and were studied for the hydrodeoxygenation (HDO) of 2-methyltetrahydrofuran (2-MTHF). The loading of the active phase was varied from 0.58, 1.16, and 1.74 to 2.3 mmol (g support)−1 and the corresponding samples were denoted as 0.5, 1.0, 1.5, and 2.0 Ni2P/USY. The two lowest loading supports did not show X-ray diffraction (XRD) lines, but X-ray absorption fine-structure spectroscopy (XAFS) indicated the formation of a Ni2P phase, with low Ni–Ni coordination, consistent with high dispersion. The two highest loading supports showed XRD patterns typical of Ni2P, and XAFS indicated similar bond distances to bulk Ni2P and high Ni–Ni coordination. Furthermore, the XAFS data indicated that the low-loading samples had shorter bond distances and more Ni in square-pyramidal coordination compared to the high loading samples and the reference Ni2P material, suggesting that there were differences in structural properties in the samples. This likely was due to preferred termination of the small crystallites with pyramidal Ni sites. The HDO of 2-MTHF was studied at 0.5 MPa and 513–593 K and the main products were n-pentane and n-butane for all catalysts. The low-loading samples showed higher turnover frequency (based on sites titrated by CO chemisorption), and this was attributed to the higher intrinsic activity of the pyramidal Ni sites. In addition, the low-loading samples showed higher selectivity to n-pentane, and this was attributed to lower C–C hydrogenolysis type reactions, which are favored by metallic ensembles as found in the high-loading samples.

Selective CO methanation over Ru/TiO2, Ru-Ni/TiO2, Ru-Co/TiO2, Ru-Fe/TiO2, Ru-La/TiO2, Ru-K/TiO2, and Ru-Ni-La/TiO2 was investigated as a CO removal method from reformate gas for polymer electrolyte fuel cell applications, and the selectivity and activity were examined. The addition of Co and La to Ru/TiO2 improved both CO and CO2 methanation, while the addition of Ni raised only the activity for CO methanation. The addition of La increased the electron density in the Ru species, which likely enhanced the dissociation of the C O bond of CO on Ru probably due to back donation of electrons from Ru to CO. This led to high CO methanation activity over Ru-La/TiO2. The trimetallic catalyst Ru-Ni-La/TiO2 showed the highest CO methanation activity among the prepared catalysts, resulting in a wider temperature range for selective CO methanation at low temperatures compared to Ru/TiO2.

Novel ultra-thin Pd and Pd-alloy (Pd–Ag, Pd–Cu) membranes, with a phosphorus component, were prepared on a porous hollow fiber α-alumina support. The aim was to study the effect of the presence of a P additive on the behavior of the membranes towards sulfur poisoning. To incorporate P in the structure, the membranes were exposed to PH 3 as a gaseous phosphorous source. The performance and sulfur resistance of the membranes with and without P was evaluated by measuring the hydrogen permeance and the H 2 /N 2 selectivity at 673 K before and during exposure to a gas mixture of 100 ppm H 2 S in H 2 , and also after regeneration in H 2 . The membranes were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), both before exposure to H 2 S and after exposure/regeneration. XRD shows no detectable amounts of sulfur or phosphorus compounds in any of the exposed or P-treated membranes respectively. XPS indicates that S was located on the surface of the H 2 S/H 2 treated Pd and Pd–Ag membranes. No S was detected on the surface of the Pd–Cu membranes indicating that no irreversible S compounds were formed in the latter. P was also detected on the surface of the P-treated membranes. The presence of phosphorus lowered the hydrogen permeance and H 2 /N 2 selectivity; however it drastically improved the Pd-alloy membranes' capacity of recovery in H 2 after H 2 S poisoning. The Pd–Cu membrane recovered only part of its H 2 permeance after regeneration, going from 11.2×10 −7 mol m −2 s −1 Pa −1 (as-prepared) to 2.3×10 −7 mol m −2 s −1 Pa −1 , while in the presence of P the H 2 permeance varied from 5.2×10 −7 mol m −2 s −1 Pa −1 (as-prepared) to 6.5×10 −7 mol m −2 s −1 Pa −1 and its H 2 /N 2 selectivity increased from 30,000 to 40,000. Similarly, the Pd–Ag membrane recovered better in the presence of P going from 17×10 −7 mol m −2 s −1 Pa −1 (as-prepared) to 6.3×10 −7 mol m −2 s −1 Pa −1 in contrast to 52×10 −7 mol m −2 s −1 Pa −1 (as-prepared) to 5.9×10 −7 mol m −2 s −1 Pa −1 in the absence of P. SEM images show that in the absence of P, more cracks and pinholes are visible on the surface of the H 2 S/H 2 exposed membranes. The presence of P produces more homogeneous surfaces and less segregation, conferring a structural integrity to the membrane by suppressing the formation of cracks and pinholes.

Bio-oil obtained by the pyrolysis of woody biomass contains many oxygenated organic compounds which degrade the product quality and make necessary upgrading for its use as a liquid fuel. Hydrodeoxygenation (HDO) is a catalytic hydrotreating process for the removal of the problematic oxygen functionalities and is promising for bio-oil upgrading. In this work, 2-methyltetrahydrofuran (2-MTHF) was chosen as a model oxygenated compound, and its HDO reaction mechanism was studied on a silica-supported nickel phosphide catalyst (Ni 2 P/SiO 2 ) at a medium pressure of 0.5 MPa. The temperature dependency of the catalyst activity was determined and it was found that at 350 °C Ni 2 P/SiO 2 showed 100% conversion and 85% selectivity to n -pentane, with higher oxygen removal activity and less C C bond cracking activity than commercial noble metal Ru/C and Pd/Al 2 O 3 catalysts based on the same amount of active sites. A contact time study allowed the determination of a reaction sequence for 2-MTHF HDO on Ni 2 P/SiO 2 and it was found that C O bond cleavage of the furanic ring to generate either 2-pentanone or 1-pentanal was the rate-determining step. This was followed by hydrogen transfer steps to produce oxygen free compounds, n -pentane or n -butane. A partial pressure analysis of 2-MTHF and H 2 was consistent with a rate equation derived using a Langmuir–Hinshelwood (L–H) mechanism. This suggested that adsorption of 2-MTHF and hydrogen occurred competitively and that these species reacted on the Ni 2 P/SiO 2 surface. Although high partial pressure of H 2 was favorable for hydrogenation, too much H 2 competed with 2-MTHF adsorption, which caused lower conversion.

Hydrogen separation membranes are important in the gas separation field and among these, silica-based membranes have emerged as promising materials at high temperatures due to their high permeation rates, high selectivity, hydrothermal stability, resistance to poisons, and mechanical strength. A critical review of the preparation of silica membranes by chemical vapor deposition (CVD) is given, with special attention placed on the two major supports used, Vycor glass and porous alumina. The coverage includes the different gas transport mechanisms that occur through silica membranes, which are convective flow, Knudsen diffusion, molecular sieving, activated diffusion, and solid-state diffusion. A description is made of the two main CVD geometries, which are the “one-sided” feed and “opposing reactants” feed configurations. The results of numerous studies in which CVD precursors such as silicon alkoxides and organosilicon species, as well as non-silicon element compounds are used to control pore size and surface properties are presented. Also the effect of varying reaction conditions such as temperature, pressure, and reaction time are compared. Finally, the permeation properties of the silica membranes are compared to those of palladium membranes, both types of membranes are employed for hydrogen separation in membrane reactors, and the advantages of silica membranes in these reactor systems are discussed.

The ethanol steam reforming (EtOH SR) reaction was carried out over a Co–Na/ZnO catalyst both in a packed bed reactor (PBR) and in membrane reactors (MRs) equipped with ultrathin Pd or Pd–Cu membranes to evaluate the benefits of employing membranes. For all conditions, ethanol conversion and hydrogen production were significantly higher in the MRs than in the PBR. Average ethanol conversion enhancement and hydrogen production enhancement were measured to be 12% and 11% in the Pd MR and 22% and 19% in the Pd–Cu MR, respectively. These enhancements of the conversion and product yield can be attributed to the shift in equilibrium by continuous hydrogen removal by the Pd based membranes. A significant contamination of the Pd layer by CO or carbon compounds during the reaction can be the reason for the comparatively low enhancement in the Pd MR compared to the Pd–Cu MR in spite of the high H 2 permeability of the original Pd membrane. A one-dimensional modeling study of the MRs and the PBR was conducted and their predicted results were compared to those obtained from the experimental study. The model was developed using a simplified power law expression but the predicted values fit the experimental data with only minor deviations. Enhancements of ethanol conversion and hydrogen yield with space velocity (SV) could be explained by the increased H 2 flux through the membranes with SV in the MRs.

Hybrid organic-inorganic H2-selective membranes consisting of single-layer or dual-layers of silica incorporating aromatic groups are deposited on a porous alumina support by chemical vapor deposition (CVD) in an inert atmosphere at high temperature. The single-layer silica membranes, which are made by the simultaneous decomposition of phenyltriethoxysilane (PTES) and tetraethylorthosilicate (TEOS), have good hydrothermal stability at high temperature and a high permeance for hydrogen in the order of 10−7 mol m−2 s−1 Pa−1 at 873 K, while preventing the passage of other larger molecular gases such as CH4 and CO2. The dual-layer silica membranes, which are obtained from the sequential decomposition of PTES and TEOS, exhibit an extremely high permeance for hydrogen of 3.6 × 10−6 mol m−2 s−1 Pa−1 at 873 K with a permselectivity of hydrogen over methane of 30. A normalized Knudsen based permeance method is applied to measure the pore size of PTES-derived silica membrane on the dual-layer silica membrane before...

The methane dry-reforming and steam reforming reactions were studied as a function of pressure (1–20 atm) at 973 K in conventional packed-bed reactors and a membrane reactors. For the dry-reforming reaction in a conventional reactor the production yield of hydrogen rose and then decreased with increasing pressure as a result of the reverse water-gas shift reaction in which the hydrogen reacted with the reactant CO2 to produce water. For the steam reforming reaction the production yield of hydrogen kept increasing with pressure because the forward water-gas shift reaction produced additional hydrogen by the reaction of CO with water. In the membrane reactors the methane conversion and the hydrogen production yields were higher for both the dry-reforming and steam reforming reactions, but for the dry reforming at high pressure half of the hydrogen was transformed into water. Thus, the dry-reforming reaction is not practical for producing hydrogen.

The effects of hydrogen permeance and selectivity in the performance of membrane reactors for the ethanol steam reforming (EtOHSR) were studied at 1–10 atm and 623 K. The studies were performed with Pd–Cu and SiO 2 –Al 2 O 3 composite membranes prepared by depositing the permselective components onto porous alumina supports with intermediate layers. The hydrogen permeances of the membranes varied from 5.2 × 10 −8 to 3.9 × 10 −6 mol m −2 s −1 Pa −1 and the selectivity ranged from 200 to 1000 (H 2 /CO 2 ) at 623 K, which allowed a broad set of conditions to be probed. Comparison studies with packed-bed reactor (PBR) and membrane reactor (MR) operation showed that higher ethanol conversions and hydrogen molar flows were obtained in the MRs for all pressures studied. It was determined that both hydrogen permeance and selectivity had a favorable effect on the EtOHSR reaction, with the highest ethanol conversion enhancement of 44% and hydrogen molar flow enhancement of 69% obtained in a MR fitted with a membrane with the highest hydrogen permeance. A criterion for the required permeance for industrial applications is developed, which for 1 cm diameter membrane tubes is 2.5 × 10 −7 mol m −2 s −1 Pa −1 .

Nickel phosphide (Ni 2 P) is an emerging catalyst for hydrodesulfurization and other important environment- and energy-related catalytic reactions. To understand its high performance, the surface structure of a Ni 2 P (0 0 0 1) single crystal surface was investigated using dynamical LEED analysis. The obtained surface structure for Ni 2 P (0 0 0 1)-1 × 1 is a P-covered Ni 3 P 2 structure (Ni 3 P_P structure) as opposed to the expected bulk terminated surface structures. This Letter discusses the driving force for the formation of the Ni 3 P_P surface, which involves the minimization of dangling bonds.

Thin and defect-free Pd–Cu composite membranes with high hydrogen permeances and selectivities were prepared by electroless plating of palladium and copper on porous alumina supports with pore sizes of 5 and 100 nm coated with intermediate layers. The intermediate layers on the 100 nm supports were prepared by the deposition of boehmite sols of different particle sizes, and provided a graded, uniform substrate for the formation of defect-free, ultra-thin palladium composite layers. The dependence of hydrogen flux on pressure difference was studied to understand the dominant mechanism of hydrogen transport through a Pd–Cu composite membrane plated on an alumina support with a pore size of 5 nm. The order in hydrogen pressure was 0.98, and indicated that bulk diffusion through the Pd–Cu layer was fast and the overall process was limited by external mass-transfer or a surface process. Scanning electron microscopy (SEM) images of the Pd–Cu composite membrane showed a uniform substrate created after depositing one intermediate layer on top of the alumina support and a dense Pd–Cu composite layer with no visible defects. Cross-sectional views of the membrane showed that the Pd–Cu composite layer had a top layer thickness of 160 nm (0.16 μm), which is much thinner than previously reported.

This review describes palladium and palladium alloy membranes for hydrogen separation prepared by different fabrication methods and using different membrane supports. Several correlations of structure and function for those membranes are provided based on mechanistic considerations of permeance along with structural properties and membrane morphologies. Particular attraction is placed in analysis of the hydrogen permeance and selectivity of membranes reported in recent papers. Composite palladium membranes prepared by the electroless plating technique deposited on alumina substrates are found to be the most promising for practical applications. It is concluded that the prospects for the use of palladium membranes in industrial applications are improving due to extensive research addressing current problems such as durability, hydrogen embrittlement, fouling by hydrocarbons or hydrosulfide compounds, and the high cost of palladium.

Ultra-thin Pd composite membranes with a thickness of 1 μm were prepared by a novel electric-field assisted activation technique followed by electroless deposition of Pd on a hollow-fiber α-alumina support. The novel activation method places Pd precursors and a reducing agent on opposite sides of a porous substrate and uses an electric field to cause migration of Pd ions to the outer surface where they are reduced to form seeds in high density in a narrow spatial region. The resulting membranes showed a high hydrogen permeance in the range of 4.0–5.0 × 10{sup −6} mol m{sup −2} s{sup −1} Pa{sup −1} and stable H{sub 2}/N{sub 2} selectivity of 3000–9000 during stability tests for 150 h at 733 K with H{sub 2} flow. The formation of the thin, defect-less and robust Pd layer can be ascribed to the evenly distributed Pd seeds on the support layer and the enhanced bonding between the Pd layer and the support layer resulting from the strong anchoring of the Pd seeds onto the support in the new activation step.

The catalytic properties of gold catalysts leached with sodium cyanide solutions were investigated for the propylene epoxidation reaction with H 2 /O 2 mixtures. Unexpectedly, the selectivity of the Au/TS-1 catalysts changed from propylene oxide to propane as a result of the cyanide treatment. Measurements by in situ X-ray absorption spectroscopy at in situ reaction conditions demonstrated that the active catalyst before leaching consisted of gold in the zero-valent state, while after the cyanide treatment had gold in the Au + state. Examination of the catalysts by high resolution transmission electron microscopy revealed the formation of precipitates of a material with lattice spacings corresponding to Na[Au(CN) 2 ]. It is found that leaching with cyanide does not result in positively-charged gold ions substituting in cation vacancies, as previously thought, but instead produces a gold(I) cyanide precipitate with catalytic hydrogenation properties typical of ptatinum. These results explain previously reported findings on highly dispersed gold nanoparticles, in which the peripheral atoms are positively charged.

The surface structure of Ni2P (1010), a model for highly active hydrodesulfurization catalysts, was studied using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) in order to understand the reconstruction of the surface layers. Annealing at 573 K revealed a (1 × 1) LEED pattern which changed to a c(2 × 4) arrangement by further heating to 723 K. Atomic scale STM images were obtained for both the (1 × 1) and c(2 × 4) structures. Bright spots observed in the STM images were interpreted to be due to surface phosphorus atoms and this was supported by a density functional theory (DFT) simulation. Several possible models for the c(2 × 4) reconstructed structures were proposed including a P-dimer defect model, a missing-row model and a missing-row + added-row model. The last model gave the best explanation for the c(2 × 4)structure. The mechanism for the c(2 × 4) reconstruction on the Ni2P (1010) surface is discussed.

An operability level coefficient ( OLC ), defined as the ratio of product permeation and product formation rates, and related to the inverse combination of the Damkohler number and the Peclet number (1/ DaPe ), is suggested as a useful tool for estimating performances of membrane reactors (MRs) operating as separators in equilibrium-limited reactions. The OLC s for product hydrogen formation in previously reported MRs for methane dry-reforming (MDR), methane steam-reforming (MSR), methanol steam-reforming (MeOHSR), and ethanol steam-reforming (EtOHSR) were correlated with conversion and yield enhancements. For values of OLC s ranging from 0.03 to 0.78, a clear universal trend for increasing conversions and hydrogen yields with increasing OLC was observed for these different types of reforming reactions. The OLC curve calculated from a numerical simulation without adjustable parameters was found to closely approximate experimental data obtained from the MRs, and was shown not to depend on the assumed kinetics. This study confirms that hydrogen selectivity (from the ratio of single-gas permeances) has a substantial influence on conversion and hydrogen yield enhancements in a MR, and demonstrates that a hydrogen selectivity of 100 is sufficient to achieve high performance in a MR.

Ni 2 P catalysts supported on SiO 2 and MCM-41 were prepared by temperature-programmed reduction (TPR), and the effect of the dispersion on catalyst structure and hydroprocessing performance was studied. The surface areas of the samples varied from low (Ni 2 P/SiO 2 -L, 88 m 2 g −1 ) to high (Ni 2 P/SiO 2 -H, 240 m 2 g −1 ), to very high (Ni 2 P/MCM-41, 487 m 2 g −1 ), with corresponding Ni 2 P average crystallite sizes decreasing from 10.1 to 6.5 and 3.8 nm. X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) studies were used to obtain structural parameters for the supported Ni 2 P phase. The catalytic activity in hydrodesulfurization (HDS) was measured at 613 K and 3.1 MPa in a three-phase fixed bed reactor using a model liquid feed containing 4,6-dimethyldibenzothiophene (4,6-DMDBT) and quinoline in a tridecane solvent. At standard conditions using 500 ppm S as 4,6-DMDBT, 6000 ppm S as dimethyldisulfide (DMDS), and 500 ppm N as quinoline, the catalytic activity followed the sequence Ni 2 P/MCM-41 > Ni 2 P/SiO 2 -H > Ni 2 P/SiO 2 -L, based on equal sites (230 μmol) loaded in the reactor. In particular, Ni 2 P/MCM-41 gave an HDS conversion of 90%, which was much higher than that of a commercial Ni–Mo–S/Al 2 O 3 catalyst which gave an HDS conversion of 68%, based on equal number of sites (230 μmol) loaded in the reactor. The sites were counted by CO chemisorption for the phosphide and by low-temperature O 2 chemisorption for the sulfide. EXAFS analysis of the samples confirmed the presence of two types of sites, tetrahedral Ni(1) sites and square pyramidal Ni(2) sites, with the latter growing in number in the same order as the reactivity Ni 2 P/MCM-41 > Ni 2 P/SiO 2 -H > Ni 2 P/SiO 2 -L, as the crystallite size decreased. From the selectivity to the direct desulfurization (DDS) product (dimethylbiphenyl) and the hydrogenation (HYD) products (methylcyclohexyltoluenes and dimethylbicyclohexyls) it is concluded that the Ni(1) sites are responsible for DDS while the Ni(2) are highly active sites for the HYD route.

A thin layer (30–40 nm) of a dual-element silica–alumina composition was deposited on a porous alumina support by chemical vapor deposition (CVD) in an inert atmosphere at high temperature. Prior to CVD, an intermediate layer of γ-alumina was coated on the macroporous alumina support. The intermediate layer was prepared by the dip-coating and calcination of boehmite sols of different sizes to give a graded structure that was substantially free of defects. The resulting supported composite membrane had high permeance for hydrogen in the order of 2–3 × 10−7 mol m−2 s−1 Pa−1 at 873 K with selectivities of H2 over CH4, CO and CO2 of 940, 700 and 590, respectively. The membrane operated by a hopping mechanism involving jumps of permeating molecules between solubility sites. The presence of aluminum improved the hydrothermal stability of the membranes for periods in excess of 500 h at 873 K in 16% steam, allowing the permeance to remain above 10−7 mol m−2 s−1 Pa−1, although with decreased selectivities.

The gas-phase epoxidation of propylene was studied over MoO x /SiO2 catalysts in a reaction system with a post-catalytic bed volume. In the reaction of a mixture of propylene and propane with oxygen below 578 K, propylene oxide (PO) was mainly formed from the oxidation of propylene. It was found that the oxidation reaction was very sensitive to the temperature of the post-catalytic space more than the temperature of the catalyst bed, strongly indicating that radical reactions occurring in the post-catalytic bed free space were responsible for the PO formation. The addition of NO increased propylene conversions and PO selectivity at low conversions, confirming that radical reactions were involved in the propylene reactions.

The kinetics of propylene oxidation to propylene oxide (PO) with H 2 /O 2 mixtures on gold supported on the mesoporous titanium silicate, Ti-TUD, was investigated using Langmuir-Hinshelwood (L-H) models and power-rate law (PRL) models. The catalyst gave stable activity and was appropriate for the kinetic studies, giving high selectivity to PO (>95%) at low conversions of propylene (

Silica supported nickel molybdenum phosphides (NiMoP/SiO2) were successfully prepared by temperature-programmed reduction (TPR) reaction of phosphorous-impregnated nickel molybdenum oxides (NiMoO4) precursors with hydrogen at relatively low temperatures (530 – 590 oC) and characterized by Fourier transform-Infrared spectrometry (FT-IR), X-ray diffraction (XRD), Electron probe microanalysis (EPMA) and Temperature-programmed reduction reaction (TPR). The process of solid transformation and properties of materials prepared from ammonium hydrogen phosphate (AMP)-impregnated samples were compared with those of phosphide made from phosphoric acid (PAC)-impregnated samples. Results show that the formation of a single NiMoP phase on silica significantly depends on reduction rates, phosphorous sources and phosphorous loadings. A single phase of NiMoP on SiO2 was particularly promoted at a below 5 oC/min of reduction rate and the starting molar ratio of Ni/Mo/P=1/1/1. A single phase of crystalline NiMoP on silica was produced from AMP-impregnated samples, while other phases of MoP, Ni2P, or NiMoP2 were appeared from PAC-impregnated samples with loading. The new phase of NiMoP2 was occurred with increasing phosphorous loading (above Ni/Mo/P=1/1/2.5) as a result of facilitated contact on the surface between the Ni-Mo bimetallic component and the phosphorous reagent

A new catalytic system consisting of titanium oxide clusters supported on silica was found for radical production at relatively low temperature (~573 K). The clusters give rise to selective oxidation products, such as propylene oxide, through gas-phase chain reactions.

In this work a series of supported Ag catalysts was studied for propylene epoxidation with molecular oxygen as the oxidant. It was found that α-Al2O3 and CaCO3 were suitable supports for propylene epoxidation and that on the latter Ag particles between 400 and 700 nm gave the highest selectivity to propylene oxide (PO). Ball-milling treatment of the CaCO3 catalyst and promotion with NaCl resulted in improved catalytic performance. The highest PO selectivity (45%) was obtained on a ball-milled catalyst with a silver loading of 56 wt.% supported on CaCO3 and promoted with 1 wt.% NaCl (Ag(56)–NaCl(1)/CaCO3). The catalysts were tested with reactant flow rates of C3H6:O2:He = 5:10:15 cm3 min−1, a gas hourly space velocity (GHSV) of 1800 h−1, a reaction pressure of 0.3 MPa, and a reaction temperature of 533 K (260 °C). Addition of 500 ppm of ethyl chloride (EtCl) to the reactant gases enhanced the stability of the Ag(56)–NaCl(1)/CaCO3 catalyst. X-ray diffraction (XRD) of the Ag(56)–NaCl(1)/CaCO3 catalyst detected the existence of AgCl in the catalyst and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy confirmed the presence of surface Ag+ species. Scanning electron microscopy showed a roughening of the Ag particles by the ball-milling treatment as well as by the addition of NaCl. The effect of NaCl on the enhancement of the catalytic performance was probably due to both physical and electronic changes in the properties of the catalyst. The NaCl not only helped increase the dispersion of the silver on the CaCO3 support, but also probably increased the quantity of electrophilic oxygen species favorable for epoxidation. In situ UV–vis spectra suggested that the rapid reduction of Ag+ species on the surface of the Ag(56)–NaCl(1)/CaCO3 catalyst could be the cause of a decline in PO selectivity observed during reaction.

Silica-supported manganese oxide catalysts with loadings of 3, 10, 15, and 20 wt % (as MnO2) were characterized with use of X-ray absorption spectroscopy and X-ray diffraction (XRD). The edge positions in the X-ray absorption spectra indicated that the oxidation state for the manganese decreased with increasing metal oxide loading from a value close to that of Mn2O3 (+3) to a value close to that of Mn3O4 (+2(2)/3). The XRD was consistent with these results as the diffractograms for the supported catalysts of higher manganese oxide loading matched those of a Mn3O4 reference. The reactivity of the silica-supported manganese oxide catalysts in acetone oxidation with ozone as an oxidant was studied over the temperature range of 300 to 600 K. Both oxygen and ozone produced mainly CO2 as the product of oxidation, but in the case of ozone the reaction temperature and activation energy were significantly reduced. The effect of metal oxide loading was investigated, and the activity for acetone oxidation was greater for a 10 wt % MnOx/SiO2 catalyst sample compared to a 3 wt % MnOx/SiO2 sample.

Supported Pd–Pt catalysts are efficient for hydrodesulfurization (HDS) and hydrodearomatization (HDA) reactions of diesel fuel and their activity varied with the kinds of supports. Concerning HDA, alumina supported catalysts showed four times higher TOF (turn over frequency) than silica supported one. In order to elucidate the difference in activity, the structural analysis of the active phase was performed. After reduction pretreatment, relatively uniform and large metallic alloy Pd–Pt particles were formed on SiO 2 , whereas, Pd and Pt atoms formed rather segregated particles on Al 2 O 3 . Subsequent X-ray absorption of fine structure (XAFS) analysis under HDS conditions showed no contribution of sulfur for SiO 2 supported catalyst, whereas, formation of sulfided metal species was observed in XAFS spectra for the Al 2 O 3 supported catalyst. It is suggested that on Pd–Pt/SiO 2 , thin sulfide layer on the metal cluster surface blocked the active sites and lowered the HDA activity. Presence of partially sulfided phase originated from rather segregated structure like Pd–Pt/Al 2 O 3 is thought to be requisite for high HDA activity.

Effective Ti catalysts were found for the vapor phase synthesis of propylene oxide, one of the most challenging reactions in heterogeneous catalysis. The observation that the reaction was enhanced by the presence of a post-catalytic bed volume indicated that the reaction occurred through a homogeneous chain reaction, likely initiated by surface radical generation. EXAFS analysis of the SiO2-supported catalysts indicated that active samples had Ti oxide clusters on the support. The catalytic activity was stable for 500-600 min, and indicated a promising catalytic system. [DOI: 10.1380/ejssnt.2006.74]

A detailed mechanistic study of acetone oxidation using ozone was performed on a 10 wt% silica-supported manganese oxide catalyst using in situ Raman spectroscopy. Two adsorbed intermediates were identified at reaction conditions: an acetone species with a band at 2930 cm −1 and an adsorbed peroxide species on the manganese oxide with a band at 890 cm −1 . Quantitative temperature-programmed desorption measurements showed that the acetone species resided on the silica support, which thus acted as a noninnocent support. The rates of the acetone and ozone reactions at 318–373 K were equally well described by the power-rate law and Langmuir–Hinshelwood expressions. Transient experiments showed that the rates of formation and reaction of the peroxide surface species did not correspond to the overall reaction rate, and it was concluded that it was not directly involved in the main reaction pathway. A mechanism is proposed involving the migration of the adsorbed acetone intermediate from the silica support to manganese centers, where it reacts with atomically adsorbed oxygen species to form complete oxidation products.

Supported manganese oxide catalysts were prepared by the impregnation of alumina foam blocks washcoated with alumina and silica. The manganese content based on the weight of the washcoats was 10 wt % calculated as MnO2. Fourier transform profiles of the Mn K-edge EXAFS spectra for these samples gave three distinctive peaks at 0.15, 0.25, and 0.32 nm and were close to the profiles of Mn3O4 and beta-MnO2. The number of surface active sites was determined through oxygen chemisorption measurements at a reduction temperature (Tred = 443 K) obtained from temperature-programmed reduction (TPR) experiments. Acetone catalytic oxidation was studied from room temperature to 573 K, and was found to be highly accelerated by the use of ozone on both catalysts with substantial reductions in the reaction temperature. The only carbon-containing product detected was CO2. The alumina-supported catalyst was found to be more active than the silica-supported catalyst in acetone and ozone conversion, with higher turnover frequencies (TOFs) for both reactions. The pressure drop through the foam was low and increased little (0.003 kPa/10 000 h(-1)) with space velocity. In situ steady-state Raman spectroscopy measurements during the acetone catalytic oxidation reaction showed the presence of an adsorbed acetone species with a C-H bond at 2930 cm(-1) and a peroxide species derived from ozone with an O-O bond at 890 cm(-1).

A series of nickel, molybdenum, and tungsten metal phosphides deposited on a carbon black support (Ni 2 P/C, MoP/C, and WP/C) were synthesized by means of temperature-programmed reduction. The samples were characterized by BET surface area, CO uptake, X-ray diffraction (XRD), elemental analysis, and extended X-ray absorption fine structure (EXAFS) measurements. The activity of these catalysts was measured at 613 K and 3.1 MPa in a three-phase, packed-bed reactor for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) with a model liquid feed containing 500 ppm sulfur as 4,6-dimethyldibenzothiophene (4,6-DMDBT), 3000 ppm sulfur as dimethyl disulfide, and 200 ppm nitrogen as quinoline. The Ni 2 P/C catalyst was found to exhibit the best hydroprocessing performance based on equal CO chemisorption sites (70 μmol) loaded in the reactor. An optimum Ni loading for HDS and HDN activity was found as 1.656 mmol g −1 (11.0 wt.% Ni 2 P) which gave an HDS conversion of 99% and an HDN conversion of 100% at a molar space velocity of 0.88 h −1 . These were much higher than those of a commercial Ni–Mo–S/γ-Al 2 O 3 catalyst which gave an HDS conversion of 68% and an HDN conversion of 94%, and a previously reported best Ni 2 P/SiO 2 catalyst which gave an HDS conversion of 76% and an HDN conversion of 92%. The use of carbon instead of silica as a support gave rise to other differences, which included smaller particle size, higher CO uptake, lessened retention of P on the support, and reduced sulfur deposition. The stability of the 11.0 wt.% Ni 2 P/C catalyst was also excellent with no deactivation observed over 110 h of time on stream. The activity and stability of the Ni 2 P/C catalyst were affected by the phosphorous content, both reaching a maximum with an initial Ni/P ratio of 1/2. EXAFS and elemental analysis of the spent samples indicated the formation of a surface phosphosulfide phase on the Ni 2 P, which was beneficial for hydrotreating activity, while the bulk structure of the phosphides was maintained during the course of reaction as revealed from the XRD patterns.

The kinetics for the initial stage of the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and dibenzothiophene (DBT) were comparatively examined over NiMo and CoMo sulfide catalysts and newly developed nickel phosphide catalysts. The HDS can proceed through an indirect hydrogenation (HYD) pathway and a direct desulfurization (DDS, or hydrogenolysis) pathway. The rate constants for the HYD and DDS pathways (k1 and k2, respectively) were estimated using a method that involved extrapolation to zero conversion for the initial selectivity ratio of primary products. The overall rate constants (k1 + k2) for 4,6-DMDBT on a catalyst weight basis (in units of 10-5 s-1 g·cat-1) at 573 K under a pressure of 20.4 atm increased in the order of CoMo sulfide (34.1) < Ni2P/USY (51.5) < Ni2P/SiO2 (66.4) < NiMo sulfide (83.2); however, the values based on active sites (in units of s-1 active site-1) ranked in a different order (CoMo sulfide (4.0) < NiMo sulfide (8.8) < Ni2P/USY (15.2) < Ni2P/SiO2 (23....

Alumina-supported molybdenum phosphide hydroprocessing catalysts, MoP/ γ -Al 2 O 3 , with weight loadings from 3.5 to 39 wt% were prepared by temperature-programmed reduction of alumina-supported molybdenum phosphate precursors. The precursors were obtained by incipient wetness impregnation of the support with aqueous molar solutions of ammonium paramolybdate and ammonium phosphate (Mo/P=1/1). Effects of loading, reduction temperature, and heating rate on the catalysts were studied, and the samples were characterized by CO chemisorption, BET surface area, and X-ray diffraction (XRD) measurements. Compared to the bulk MoP and MoP/SiO 2 systems (which are similar to one another), the MoP/ γ -Al 2 O 3 material showed different behavior. Whereas calcined bulk and silica-supported molybdenum phosphates form Mo–P amorphous glasses which reduce directly to MoP, for the alumina-supported phosphates at high loadings (e.g., 13 wt% MoP/ γ -Al 2 O 3 ), a MoO 3 component is visible which reduces sequentially with temperature to MoO 2 and Mo metal, and then transforms to MoP. The difference in behavior between these systems is attributed to the formation of a strongly bound amorphous phosphate surface layer on the alumina support. Alumina has a strong affinity for phosphates, and appears to initially abstract a substantial amount of phosphorus from the stoichiometric molybdenum phosphate mixture. The alumina then releases the phosphorus at high temperature, allowing it to recombine with Mo metal to form MoP and generating active sites. The MoP/ γ -Al 2 O 3 catalysts performed well in hydroprocessing of a simulated distillate containing dibenzothiophene and quinoline at conditions representative of industrial hydroprocessing (643 K, 3.1 MPa). For the 13 wt% sample the hydrodesulfurization conversion was 57% and hydrodenitrogenation conversion was 62%. Catalytic activity, based on equal chemisorption sites loaded in the reactor (70 μmol), was generally independent of the amount of MoP deposited on the alumina surface, independent of the presence of X-ray visible molybdenum phases, and was associated with a relatively high temperature reduction peak found at all loading levels of MoP/Al 2 O 3 but not in bulk MoP. We conclude that the high-temperature peak gives rise to highly dispersed MoP which is responsible for the bulk of the CO titration sites and the catalytic activity, and that the large MoP particles visible by XRD make smaller contributions.

A series of iron, cobalt, and nickel metal phosphides of chemical formula Fe2P, CoP, and Ni2P with specific surface areas of around 3 m2 g−1 were synthesized by means of temperature-programmed reduction (TPR) of the corresponding phosphates. These phosphides were also successfully prepared in dispersed form on a silica support (90 m2 g−1) for use as catalysts. The phase purity of these materials was established by X-ray diffraction (XRD), and surface properties were determined by N2 BET specific surface area (Sg) measurements and CO uptake determinations. The activity of the silica-supported catalysts in hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) was evaluated in a three-phase trickle-bed reactor using a model liquid feed containing 2000 ppm nitrogen as quinoline, 3000 ppm sulfur as dibenzothiophene, 500 ppm oxygen as benzofuran, 20 wt% aromatics as tetralin, and balance aliphatics as tetradecane. The reactivity study showed that the HDS activity sequence for the three samples was Ni2P/SiO2>CoP/SiO2>Fe2P/SiO2, while the HDN activity followed the sequence CoP/SiO2>Ni2P/SiO2>Fe2P/SiO2. Compared with a commercial Ni–Mo–S/γ-Al2O3 catalyst, Ni2P/SiO2 had a higher HDS activity (90 vs 76%), but a lower HDN activity (14 vs 38%), based on equal sites loaded in the reactor. The sites were determined by CO chemisorption for the phosphide and low-temperature O2 chemisorption for the sulfide. XRD and X-ray photoelectron spectroscopy characterizations of the spent catalysts indicated that the Ni2P/SiO2 catalyst was tolerant of sulfur.