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This paper describes properties of molybdenum carbides as a potential catalyst for fast pyrolysis bio-oil hydroprocessing. Currently, high catalyst cost, short catalyst lifetime, and lack of effective regeneration methods are hampering the development of this otherwise attractive renewable hydrocarbon technology. A series of metal-doped bulk Mo carbides were synthesized, characterized, and evaluated in sequential low-temperature stabilization and high-temperature deoxygenation of a pine-derived bio-oil. During a typical 60 h run, Mo carbides were capable of upgrading raw bio-oil to a level suitable for direct insertion into the current hydrocarbon infrastructure with residual oxygen content and total acid number of upgraded oils below 2 wt % and 0.01 mg KOH g–1, respectively. The performance was shown to be sensitive to the type of metal dopant, Ni-doped Mo carbides outperforming Co-, Cu-, or Ca-doped counterparts; a higher Ni loading led to a superior catalytic performance. No bulk oxidation or other sig...

Support plays a complex role in catalysis by supported metal oxides and the exact support effect still remains elusive. One of the approaches to gain fundamental insights into the support effect is to utilize model support systems. In this study, we employed for the first time titania nanoshapes as the model supports and investigated how the variation of surface structure of the support (titania, TiO2) impacts the catalysis of supported oxide (vanadia, VOx). TiO2 truncated rhombi, spheres and rods were synthesized via hydrothermal method and characterized with XRD and TEM. These TiO2 nanoshapes represent different mixtures of surface facets including [1 0 1], [0 1 0] and [0 0 1] and were used to support vanadia. The structure of supported VOx species was characterized in detail with in situ Raman spectroscopy as a function of loading on the three TiO2 nanoshapes. Oxidative dehydrogenation (ODH) of isobutane to isobutene was used as a model reaction to test how the support shape influences the activity, selectivity and activation energy of the surface VOx species. It was shown that the shape of TiO2 support does not pose evident effect on either the structure of surface VOx species or the catalytic performance of surfacemore » VOx species in isobutane ODH reaction. Finally, this insignificant support shape effect was ascribed to the small difference in the surface oxygen vacancy formation energy among the different TiO2 surfaces and the multi-faceting nature of the TiO2 nanoshapes.« less

We investigated the structural evolution of molybdenum carbides subjected to hot aqueous environments and their catalytic performance in low-temperature hydroprocessing of acetic acid. While bulk structures of Mo carbides were maintained after aging in hot liquid water, a portion of carbidic Mo sites were converted to oxidic sites. Water aging also induced changes to the non-carbidic carbon deposited during carbide synthesis and increased surface roughness, which in turn affected carbide pore volume and surface area. The extent of these structural changes was sensitive to the initial carbide structure and was lower under actual hydroprocessing conditions indicating the possibility of further improving the hydrothermal stability of Mo carbides by optimizing catalyst structure and operating conditions. Mo carbides were active in acetic acid conversion in the presence of liquid water, their activity being comparable to that of Ru/C. The results suggest that effective and inexpensive bio-oil hydroprocessing catalysts could be designed based on Mo carbides, although a more detailed understanding of the structure-performance relationships is needed, especially in upgrading of more complex reaction mixtures or real bio-oils.

In this study, alkali doped fullerenes synthesized by two different solvent assisted mixing techniques are compared for their hydrogen uptake activity. In particular, we investigated the interaction of hydrogen with lithium and sodium doped fullerenes via physisorption. In addition, we present the first mass spectrometric evidence for the formation of C 60 H 60 via chemisorption. Hydrogen physisorption isotherms up to 1 atm at temperatures ranging from 77 K to 303 K were measured demonstrating an increase in hydrogen uptake versus pure C 60 and increased isosteric heats of adsorption for the lithium doped fullerene Li 12 C 60 . The hydrogen uptake in Na 6 C 60 , Li 6 C 60 , and Li 12 C 60 was enhanced compared to pure C 60 . However, despite these improvements the low amount of physisorbed hydrogen at 1 atm and 77 K in these materials suggests that fullerenes do not possess enough accessible surface area to effectively store hydrogen due to their close packed crystalline nature.

Fullerene-derived buckybowl fractions dispersed on mesoporous silica constitute an ideal model for studying the catalysis of graphitic forms of carbon since the dispersed carbon nanostructures contain a high ratio of edge defects and curvature induced by non-six-membered rings. Dispersion of the active centers on an easily accessible high surface area material allowed for high density of surface active sites associated with oxygenated structures. This report illustrates a facile method of creating model polycyclic aromatic nano-structures that are not only active for alkane C–H bond activation and oxidative dehydrogenation but also can be practical catalysts to be eventually used in industry.

The active sites and kinetics of dry reforming of methane (DRM) on lanthanum zirconate (LZ) pyrochlore catalysts are studied as a function of Rh substitution, temperature, and partial pressures of CH4 and CO2. In this work, we focus specifically on determining the catalytic active sites for CH4 and CO2 activation and their role in the DRM mechanism over the two Rh-substituted pyrochlores, i.e., 2 wt% Rh, designated L2RhZ and 5 wt% Rh, designated L5RhZ. Kinetic rate modeling suggests dual-site mechanism, where CH4 and CO2 are activated on different sites (dual-site mechanism). Eleven different rate models were tested against the kinetic rate data obtained over these two Rh pyrochlores. Statistical analysis shows valid and similar fits for only two of eleven models: one in which activation of CH4 is rate-determining and one in which CO2 activation is rate-determining. This dual-site mechanism is studied further in detail to test the validity of the intermediate steps predicted by the kinetic model. CH4/CD4 isotope switching shows a strong deuterium kinetic isotope effect on CH4 and CO2 conversion, suggesting that CH4 dissociation is the rate-determining step. Higher apparent activation energies of CH4 (Ea, CH4) versus CO2 (Ea, CO2) on both catalysts also confirm that CH4 activation is rate-determining. Basic nature of La–O sites activates mildly acidic CO2 to form La2O2CO3 complexes as confirmed by FTIR. From different polymorphs of La2O2CO3, the spectator and reactive species were distinguished by pulsing CH4 over La2O2CO3. Alternating pulses (CH4/Ar → CO2/Ar → CH4/Ar) at 550 °C showed simultaneous formation of CO and H2, suggesting that surface carbon, formed by CH4 decomposition, is oxidized by H2O; a crucial step in understanding the catalytic behavior of pyrochlores in the reaction mechanism. These experiments were used to identify the two types of sites taking part in the dual-site DRM mechanism. The work reported here helps in determining a single set of kinetically significant steps that most closely represent the mechanistic scheme of DRM over L2RhZ and L5RhZ.

The general consensus in the studies of nanostructured carbon catalysts for oxidative dehydrogenation (ODH) of alkanes to olefins is that the oxygen functionalities generated during synthesis and reaction are responsible for the catalytic activity of these nanostructured carbons. Identification of the highly active oxygen functionalities would enable engineering of nanocarbons for ODH of alkanes. Few-layered graphenes were used as model catalysts in experiments to synthesize reduced graphene oxide samples with varying oxygen concentrations, to characterize oxygen functionalities, and to measure the activation energies for ODH of isobutane. Periodic density functional theory calculations were performed on graphene nanoribbon models with a variety of oxygen functionalities at the edges to calculate their thermal stability and to model reaction mechanisms for ODH of isobutane. Comparing measured and calculated thermal stability and activation energies leads to the conclusion that dicarbonyls at the zigzag edges and quinones at armchair edges are appropriately balanced for high activity, relative to other model functionalities considered herein. In the ODH of isobutane, both dehydrogenation and regeneration of catalytic sites are relevant at the dicarbonyls, whereas regeneration is facile compared with dehydrogenation at quinones. The catalytic mechanism involves weakly adsorbed isobutane reducing functional oxygen and leaving as isobutene, and O2 in the feed, weakly adsorbed on the hydrogenated functionality, reacting with that hydrogen and regenerating the catalytic sites.

We report the growth of a nanospiked, carbon thin film electrode by an inexpensive, non-catalytic plasma enhanced CVD process on Si substrates. The electron transfer kinetics for various redox probes of these carbon nanospikes (CNS) were determined and compared with glassy carbon and CNS exposed to oxygen plasma or a high temperature ammonia soak. The results indicate that CNS can be used as a practical alternative to GC for various electroanalysis applications. These electrodes also exhibited activity and stability toward the oxygen reduction reaction, suggesting there potential use as electrocatalyst supports. Finally, the ability to deposit conformal thin films of CNS on a 3-D architecture for use as an electrode was demonstrated. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0891409jes] All rights reserved.

In this work, we studied how TiO2 and ZrO2 coatings enhance the CO oxidation performance of SiO2-supported Pt catalysts under conditions relevant to automotive emissions control. SiO2 was coated with metal oxides TiO2 or ZrO2 by sol-gel method and the subsequent Pt loading was done by incipient wetness method. The prepared catalysts Pt/TiO2-SiO2 and Pt/ZrO2-SiO2 were compared with Pt/SiO2 and Pt/Al2O3 in fresh, sulfated, and hydrothermally aged states. The structure of the catalysts was characterized with BET, XRD, TEM, EDS, EXAFS, XANES, TPD and TPR to help interpret the CO oxidation performance. Higher dispersion, stability, and oxidation state of Pt were achieved on TiO2-SiO2 and ZrO2-SiO2 supports due to stronger metal-support interaction leading to superior CO oxidation performance compared to Pt/SiO2 and Pt/Al2O3. TiO2 and ZrO2 coatings introduced surface acidity but negligible basicity, which is a likely reason for the weak and low adsorption of SO2. The results suggest that the sol-gel coating of SiO2 with metal oxides could be an attractive strategy for designing automotive oxidation catalysts with enhanced performance such as low-temperature activity, sulfur tolerance, and hydrothermal stability.

We investigated the impact of ZrO 2 on the performance of palladium-based oxidation catalysts with respect to low-temperature activity, hydrothermal stability, and sulfur tolerance. Pd supported on ZrO 2 and SiO 2 were synthesized for a comparative study. Additionally, in an attempt to maximize the ZrO 2 surface area and improve sulfur tolerance, a Pd support with ZrO 2 -dispersed onto SiO 2 was studied. The physicochemical properties of the catalysts were examined using ICP, N 2 sorption, XRD, SEM, TEM, and NH 3 -, CO 2 -, and NO x -TPD. The activity of the Pd catalysts were measured from 60 to 600 °C in a flow of 4000 ppm CO, 500 ppm NO, 1000 ppm C 3 H 6 , 4% O 2 , 5% H 2 O, and Ar balance. The Pd catalysts were evaluated in fresh, sulfated, and hydrothermally aged states. Overall, the ZrO 2 -containing catalysts showed considerably higher CO and C 3 H 6 oxidation activity than Pd/SiO 2 under the reaction conditions studied. The good performance of ZrO 2 -containing catalysts appeared to be due in part to high Pd dispersion resulting from strong Pd and support interaction. Another beneficial effect of strong interaction between Pd and ZrO 2 was manifested as a greater hydrothermal stability with good oxidation activity even after aging at 800 and 900 °C for 16 h. In contrast, Pd/SiO 2 suffered significant performance loss due to Pd particle coarsening. Although the Pd/ZrO 2 -SiO 2 catalyst was not more active than Pd/ZrO 2 , improved tolerance to sulfur was realized. Unlike the bulk ZrO 2 support, the ZrO 2 -incorporated SiO 2 presented only weak basicity leading to a superior sulfur tolerance of Pd/ZrO 2 -SiO 2 . These results confirmed the potential of developing Pd-based oxidation catalysts with enhanced low-temperature activity and durability using ZrO 2 -SiO 2 supports. Controlling morphology and accessible area of the dispersed ZrO 2 layer appeared critical to further maximize the catalytic performance.

The support effect has long been an intriguing topic in catalysis research. With the advancement of nanomaterial synthesis, the availability of faceted oxide nanocrystals provides the opportunity to gain unprecedented insights into the support effect by employing these well-structured nanocrystals. In this Letter, we show by utilizing ceria nanoshapes as supports for vanadium oxide that the shape of the support poses a profound effect on the catalytic performance of metal oxide catalysts. Specifically, the activation energy of VOx/CeO2 catalysts in oxidative dehydrogenation of isobutane was found to be dependent on the shape of ceria support, rods < octahedra, closely related to the surface oxygen vacancy formation energy and the numbe of defects of the two ceria supports with different crystallographic surface planes.

Co–Cu–ZnO nanowire/tube catalysts were synthesized using pulse electrodeposition technique from a single aqueous electrolyte solution using a template synthesis technique. They were then tested as catalysts for the hydrogenation of CO to alcohols and higher hydrocarbons. Nanowires/tubes were grown inside the pores of membranes using a three-step sequential deposition process. First, a low current of −6.9 mA/cm2 was applied for 300 ms for Cu deposition, then a high current density of −11.5 mA/cm2 for t ms (t = 500, 600, 750 ms) was applied for Co deposition, and finally no current was applied for 1200 ms so that the ions near the cathode replenish. The surface had a significantly different composition than the bulk. On the surface, there was more Co, less Cu, and more Zn. The catalyst showed the alcohol (C1–C4) selectivity of 20.9 %C at H2/CO = 3/1, GHSV = 16 000 scc/h gcat, temperature = 270 °C, pressure = 15 bar, and time-on-stream = 65 h.

Graphitic mesoporous carbon (GMC), prepared through high-temperature graphitization of soft-templated amorphous mesoporous carbon (AMC), was used as the support for Mn, Li, and Fe triple-promoted Rh catalysts for CO hydrogenation to ethanol. The use of GMC results in C2H5OH selectivity and formation rate comparable to nonporous SiO2 support along with a significant inhibition on the formation of undesired CH4 and light hydrocarbons at the expense of appreciable amounts of CO2 produced. The better catalytic performance of promoted-Rh/GMC than those supported on other carbon allotropes (AMC and non-porous graphitic carbon black) seems to be associated with the specific graphitic structure and mesoporosity of GMC. The surface modification of GMC by wet oxidation leads to considerable increases in C2H5OH selectivity and formation rate. The modified GMC as a support shows substantially greater CO2-free selectivity for C2H5OH than the SiO2.

In this paper, a solid molecular basket sorbent, 50 wt% PEI/SBA-15, was studied for CO(2) capture from gas streams with low CO(2) concentration under ambient conditions. The sorbent was able to effectively and selectively capture CO(2) from a gas stream containing 1% CO(2) at 75 °C, with a breakthrough and saturation capacity of 63.1 and 66.7 mg g(-1), respectively, and a selectivity of 14 for CO(2)/CO and 185 for CO(2)/Ar. The sorption performance of the sorbent was influenced greatly by the operating temperature. The CO(2)-TPD study showed that the sorbent could be regenerated under mild conditions (50-110 °C) and was stable in the cyclic operations for at least 20 cycles. Furthermore, the possibility for CO(2) capture from air using the PEI/SBA-15 sorbent was studied by FTIR and proved by TPD. A capacity of 22.5 mg g(-1) was attained at 75 °C via a TPD method using a simulated air with 400 ppmv CO(2) in N(2).

The effect of Li and Mn promoters on the structure and selectivity of supported Rh catalysts for CO hydrogenation reaction was examined. Infrared spectroscopy and X-ray absorption were used to inve...

Graphitic mesoporous carbon was modified with phosphorous heteroatoms in order to tune the catalytic selectivity and to investigate the roles of different oxygen species for the oxidative dehydrogenation reaction of isobutane to isobutene. Small changes in the isobutane apparent activation energy are consistent with the notion that the phosphorous groups do not change the nature of the active sites but they interfere with the availability of the sites. Our results show that the improvement on selectivity is not proportional to the amount of phosphorous added. Small phosphorous content improved the selectivity by suppressing the combustion of isobutane. However, a higher amount of phosphorous groups lead to coverage of selective quinone sites and/or creation of active sites favorable to total oxidation.

Cobalt−rhenium based catalysts were prepared by coimpregnation from two different cobalt precursors: cobalt nitrate [CoRe(N)] and cobalt acetate [CoRe(A)]. They were characterized by H2-TPR, ICP, X...

The addition of 0.10 wt% Li to Rh/TiO2 more than doubled the CO conversion for CO hydrogenation while increasing ethanol selectivity. The addition of Li also increases formation of C2 oxygenates at the expense of C1 species, methanol and methane. This is attributed to enhanced dispersion of Rh by Li that appears to reduce dissociation of CO, which previous studies have shown requires large ensembles of Rh atoms on the surface. Li promotion appears to increase the associatively adsorbed CO, allowing for increased H2 chemisorption on the surface compared to the dissociative adsorption of the same number of CO atoms. This increases selectivity to ethanol compared to the unpromoted catalysts. CO-TPD shows more reactive adsorbed CO species on the Li-promoted catalyst. FTIR results suggest that Li promotion alters CO bonding at bridged or interfacial sites and its effect is more structural than electronic.

Reaction network analysis of the oxidative dehydrogenation (ODH) reaction of isobutane over model carbon catalysts with tailored open-edge graphitic structure and quinone-type oxygenated functionalities was used to identify the selective pathways for the formation of isobutene. Carbon-based materials have been widely used in catalysis, but the active sites are not well-understood due to the complexity of the carbon structure. Correct identification of these sites is essential for learning how to manipulate material structure to achieve high catalytic yields of the desired products. In this study, we created model catalysts with controllable surface concentration of oxygen based on graphitized mesoporous carbon (GMC). Our studies reveal that the ODH reaction of isobutane on carbon catalysts is a parallel-consecutive pathway with partial oxidative dehydrogenation for the formation of isobutene and deep oxidation pathway for the direct formation of CO and CO2 from isobutane. These two pathways show different dependence on the quinone-type oxygen sites: the rate constant leading to the desired partial oxidation product does not show a strong correlation to the density of the oxygen sites, whereas the rate constant leading to the unselective COx products increases continuously with the density of oxygen sites.

In situ FTIR spectroscopy coupled with downstream mass spectrometry has been used to clarify the pathways for room temperature (rt) CO oxidation over iron phosphate-supported Au catalyst. The charge state of Au on Au/FePO4 after calcination, reduction, or under reaction conditions was assessed by both FTIR spectroscopy (CO probing) and X-ray absorption near edge spectroscopy (XANES). Results from both approaches show that cationic gold species dominate the surface after pretreatment in O2 at 200 °C. A portion of the cationic gold on Au/FePO4 can be reduced by the initial CO adsorption at rt, and subsequently repeated CO exposures do not reduce the remaining cationic Au. FTIR and Raman results from cycled CO reduction and O2 reoxidation of Au/FePO4 indicate that there are active structural oxygen species on the surface of Au/FePO4that can be consumed by CO and then replenished by gaseous O2 at rt. Au activates both CO and O2 so that the FePO4 support can undergo reduction (by CO) and reoxidation (by O2) cycles. The results of CO oxidation with labeled 18O2 suggest the operation of two parallel reaction pathways at rt: (1) a redox pathway in which FePO4 supplies active oxygen and (2) a direct pathway on metallic Au, via either Langmuir–Hinshelwood or Eley–Rideal mechanism, in which gas phase O2 provides the active oxygen.

Two activated carbons of different origin were impregnated with the solution of sodium hydroxide (NaOH) of various concentrations up to 10 wt %, and the effect of impregnation on the catalytic performance of the carbons was evaluated. The catalytic activity was analyzed in terms of the capacity of carbons for hydrogen sulfide (H2S) conversion and removal from hydrogen-rich fuel streams and the emission times of H2S and the products of its oxidation [e.g., sulfur dioxide (SO2) and carbonyl sulfide (COS)]. The results of impregnation showed a significant improvement in the catalytic activity of both carbons proportional to the amount of NaOH introduced. NaOH introduces hydroxyl groups (OH−) on the surface of the activated carbon that increase its surface reactivity and its interaction with sulfur-containing compounds.

2.5 nm gold nanoparticles were grown on a fumed silica support, using the physical vapor deposition technique of magnetron sputtering, that are thermally stable when annealed in an oxygen containing environment up to at least 500 °C. Traditional Au/TiO 2 catalysts rapidly sinter to form large 13.9 nm gold clusters under these annealing conditions. This surprising stability of Au/SiO 2 is attributed to the absence of residual impurities (ensured by the halide-free production method) and a strong bond between gold and defects at the silica surface (about 3 eV per bond) estimated from density functional theory (DFT) calculations. The Au/SiO 2 catalysts are less active for CO oxidation than the prototypical Au/TiO 2 catalysts, however they can be regenerated far more easily, allowing the activity of a catalyst to be fully recovered after deactivation.

In this communication, we report the synthesis of NiAu alloy nanoparticles (NPs) and their use in preparing Au/NiO CO oxidation catalysts. Because of the large differences in Ni and Au reduction potentials and the immiscibility of the two metals at low temperatures,1, 2 NiAu alloy NP colloids are inherently difficult to prepare by reducing metal salts with common reducing agents. This study describes the first solution-based synthesis of NiAu alloy NPs by way of a fast butyllithium reduction method. By supporting the particles on SiO2 and subsequent conditioning, one obtains a NiO-stabilized Au NP catalyst that exhibits remarkable resistance to sintering and is highly active for CO oxidation. The active NiO-stabilized Au NP catalyst is prepared by in situ phase transformation of NiAu alloy NPs through an Au@Ni core-shell like NP intermediate. In contrast, the corresponding NiO-free Au NPs prepared by an analogous method show negligible low-temperature catalytic activity and a high propensity for coalescence.

The hydrothermal Mo−V-based mixed oxide catalysts possessing the M1-phase structure were investigated by XANES and in situ X-ray diffraction under ambient and dynamic redox conditions in the presence of O2 and H2 at 693 K. Under ambient conditions, XANES, with the use of model compounds, suggested oxidation states of Nb, Te, Mo, and V close to 5+, 4+, 6+, and 4+, respectively, in the bulk M1 phase. The oxidation state changes of Nb, Te, and Mo were not detected under the dynamic redox conditions employed, while the pre-edge peak of vanadium in the M1 phase exhibited small, reproducible shifts, suggesting that VOx is the active catalytic species in the bulk M1-phase catalysts for selective (amm)oxidation of propane.

Dendrimer-metal-nanocomposites (DMNs) were used as precursors to prepare SiO2-supported monometallic Pt, Cu, and bimetallic Pt–Cu catalysts with Pt/Cu atomic ratios of 1:1 (Pt50Cu50) and 1:3 (Pt25Cu75). After impregnation of these DMNs onto the support, the catalysts were thermally treated and activated following an optimized protocol. Scanning transmission electron microscopy (STEM) showed that the metal nanoparticles in the dendrimer-derived SiO2-supported catalysts were smaller and had a narrower size distribution compared with those in conventional catalysts prepared using corresponding metal salts via the wet-impregnation method. Slow deactivation was observed for hydrodechlorination of 1,2-dichloroethane over monometallic Cu catalysts, which showed an activity about one to two orders of magnitude lower than that of the Pt-containing catalysts. Hydrodechlorination of 1,2-dichloroethane over the Pt and Pt50Cu50 catalysts produced mainly ethane, and the selectivity toward ethane increased with temperature. For the Pt25Cu75 catalyst, the selectivity toward ethane decreased in favor of that of ethylene. The overall activity decreased with increasing Cu loading in the catalysts. Activity based on surface Pt sites suggests the formation of bifunctional surfaces in Pt25Cu75 catalyst favoring C Cl bond scission on Cu sites and hydrogenation of intermediate ⋅CH2CH2⋅ on Pt sites. In addition, kinetic analyses suggest different reaction mechanisms for hydrodechlorination of 1,2-dichloroethane over Pt and Cu-enriched surfaces in the Pt–Cu bimetallic catalysts.

Catalysts derived from non-thermal plasma techniques have previously shown unusual and highly advantageous catalytic properties including room temperature reduction, unusual metal particle structure and metal-support interactions, and enhanced selectivity and stability. This study focuses on the characterization of Al2O3 supported Ni catalysts derived from the RF non-thermal plasma technique with in-situ XRD, TPR-MS and STEM and on relating the results to the enhanced activity and stability of benzene hydrogenation. The results suggest that catalysts with plasma treatments before impregnation are relatively easier to be reduced and result in better activities under mild reduction conditions. These plasma treatments stabilize the nickel particle sizes of air(B) and H2(B) catalysts at 600 °C by slowing down the sintering process. Plasma treatments after the impregnation of precursors, on the other hand, tend to delay the growth of nickel particles below 600 °C, forming smaller Ni particles, but with a sudden increase in particle size near 600 °C. It suggests that the structure of Ni nitrate and the metal-support interaction have been altered by the plasma treatments. The reduction patterns of plasma treated catalysts are, therefore, changed. The catalyst with a combination plasma treatment demonstrates that the effect of a combination plasma treatment is larger than either the plasma treatment before or after the impregnation alone. Both plasma treatments before and after the impregnation of metal precursor play important roles in modifying supported metal catalysts.

X-ray absorption spectroscopy (XAS) was utilized to investigate both the Au particle size on several supports composed by silica and titanium oxide, and the coordination of TiO2 in the support phase. Particularly, we wanted to utilize the technique to probe mixing in the support phase, by using different synthetic methods such as by functionalizing silica or by ALD (atomic layer deposition) techniques as prepared in our laboratories, and the growth and stability of Au nanoparticles deposited on these supports. The study using cosynthesis techniques to dope bulk mesoporous SiO2 with TiO2 resulted in TiO2 being dispersed in the SiO2 matrix; however, a second phase starts forming as the TiO2 content increases as indicated by the EXAFS Ti−O shell shift in position and increase of coordination number. On the supports prepared by cosynthesis, Au particles were smaller and more stable. The study using the surface sol−gel technique for deposition of single monolayers of an oxide such as TiO2 produced Ti environme...

The catalytic oxidation of hydrogen sulphide (H 2 S) on various activated carbon materials was studied. The effects of pore structure, surface characteristics, and nitrogen content on the activity and selectivity of the carbons towards oxidation of H 2 S were investigated. It was found that a high volume of both micropores and small mesopores, in combination with a relatively narrow pore size distribution, were crucial for the retention of sulphur dioxide (SO 2 ), a by-product of H 2 S oxidation. For the retention of carbonyl sulphide (COS), another H 2 S oxidation by-product, high surface reactivity with a significant amount of basic groups were found to be important. The only carbon with all these characteristics, and consequently the carbon that was able to retain both H 2 S and COS for an extended period of time, was an experimental product, “WSC”. This carbon was found to be superior to the other carbons studied, exhibiting high activity and selectivity for oxidation of H 2 S to sulphur. H 2 S breakthrough capacities and selectivity values of the carbons were found to be dependent on the nitrogen content of the carbons. In a hydrogen stream, carbons possessing the highest nitrogen contents exhibited the greatest H 2 S breakthrough capacities but, at the same time, the lowest selectivity with respect to sulphur formation. In reformate streams, the maximum breakthrough capacity and greatest selectivity were exhibited by carbons with a nitrogen content of about 1–1.5 wt%.

The size dependence of activity in gold catalysts was examined. Extended X-ray absorption fine structure was used to determine mean particle size, and a flow reactor was used to assess activity of the catalysts for CO oxidation as a function of temperature. A sequence of calcination steps was used to systematically increase the mean Au particle size while repeated measurements of the activity were conducted. In this way the size dependence could be obtained in a single catalyst to avoid differences due to variations in support, synthesis conditions, Au loading, or incidental impurities. Two Au catalysts with different Au loadings were prepared on TiO{sub 2} by deposition precipitation and used for the measurements. For Au particles with mean particle size, d, in the range of 2-10 nm, the measured TOF at 298 K varies as d{sup -1.7{+-}0.2} and d{sup -0.9{+-}0.2} for the 7.2 and 4.5 wt% Au/TiO{sub 2} (P25) catalysts, respectively. Variation between samples emphasizes the conclusion that the activity is sensitive to many factors that may mask the true structure dependence. It is concluded that the observed decrease in activity with increasing particle size beyond 2 nm is controlled by the population of low-coordinate sites, rather than by size-dependentmore » changes in overall electronic structure of the nanoparticle. No evidence was found for maximum activity for small particle sizes, although arguments are offered for why such a maximum was expected but was not observed.« less

The removal of low concentrations of hydrogen sulfide (H{sub 2}S) from hydrogen-rich gaseous fuels by selective catalytic oxidation, using activated carbon as the catalyst, was studied. The capacities of four activated carbons for reducing the H{sub 2}S concentration down to the parts per billion (ppb) level were determined to be strongly related to their microstructures and impurities, even though their activity and selectivity were strongly dependent on the test conditions, such as reaction temperature, O{sub 2}:H{sub 2}S ratio, space velocity, and length-to-diameter (L/D) ratio of the catalyst bed. Because the side reactions that form COS and SO{sub 2} are sometimes unavoidable under real fuel processing conditions, the complete and exclusive conversion of H{sub 2}S to elemental sulfur (S) requires that activated carbon has catalytic activities not only for the oxidation of H{sub 2}S, but also for the oxidation of COS and the reaction between H{sub 2}S and SO{sub 2}. Because one of the activated carbons (sample W-22) had such catalytic functions and a relatively large capacity of trapping sulfur in its micropores, this carbon showed a combination of excellent activity and selectivity on removing H{sub 2}S from both hydrogen and simulated reformate streams at a reaction temperature of {approximately} 150{supmore » o}C. 46 refs., 8 figs., 4 tabs.« less

The effect of synthesis and reaction conditions on the structure and activity of Au clusters supported on nanocrystalline and mesoporous TiO2 was investigated. X-ray absorption spectroscopy was applied to correlate the particle size and the oxidation state with several parameters, such as pH of the precursor solution, Au loading, pretreatment, and support structure. The study using mesoporous TiO2 as the support shows that lower Au loadings resulted in bigger Au aggregates with lower reducibility. The high activity state for Au supported in different allotropic forms of TiO2 corresponds to Au in a fully reduced state. Furthermore, once reduced, no reoxidation occurs under reaction conditions, even after flowing air at higher temperatures (150 and 300 °C). Therefore, our results indicate that oxidized Au is not necessary for high activity. The activity decreased with particle growth, and, compared to the other allotropic TiO2, Au on brookite exhibited no significant particle agglomeration and was the most ...

The effect of fluorine on the structure of sulfided W/Al2O3 and NiW/Al2O3 catalysts was studied by means of EXAFS on the W LIII-edge and Ni K-edge. In the WO3/Al2O3 catalyst, prepared from ammonia ...

A series of carbide and sulfide catalysts comprising NbMo 2 C, Mo 2 C, NbC and MoS 2 /SiO 2 was used to study the pyridine hydrodenitrogenation (HDN) network below at high pressure (3.1 MPa) as a function of temperature. pyridine → k 1 piperidine → k 2 n- pentylamine → k 3 hydrocarbons All the catalysts showed the same trend in activities for the three molecules: the reactivity of n -pentylamine was high, while those of piperidine and pyridine were relatively low, especially at low temperatures. The carbide catalysts showed higher selectivity towards HDN products than the sulfide catalyst at the same conversion levels. The higher selectivity was related to the higher ratio ( r = k 2 / k 1 ) between the rate constants of the two consecutive reactions, hydrogenation of pyridine ( k 1 ) and ring opening of piperidine ( k 2 ). The order of activity of the carbides and sulfide differed considerably depending on the substrate. At the same temperature, the sulfide was more active for pyridine HDN when compared to the carbide catalysts, but it was much less active for quinoline HDN, suggesting that the HDN reaction mechanism depends greatly on the structure of the N-containing molecule. However, for the pyridine reaction network the similarity in product distribution suggested that the active surface of the carbides and sulfide was similar at reaction conditions.

Preface Part I: General Aspects 1. Design of Heterogeneous Catalysts for Fuels and Chemicals Processing: An Overview Juan J. Bravo-Suarez, Raghunath V. Chaudhari, and Bala Subramaniam Part II: Computer-Aided Design 2. Computational Studies of Structure and Catalytic Activity of Vanadia for Propane Oxidative Dehydrogenation Lei Cheng and Larry A. Curtiss 3. Molecular Simulation of Carbon Capture in a Series of Isoreticular Zeolitic Imidazolate Materials Yao Houndonougbo Part III: Spectroscopic Characterization 4. Utilizing Surface Enhanced Raman Spectroscopy for the Study of Interfacial Phenomena: Probing Interactions on an Alumina Surface Eric V. Formo, Zili Wu, Shannon M. Mahurin, and Sheng Dai Part IV: Kinetics-Aided Design 5. Interactions of Sulfur Oxides with Diesel Oxidation Catalysts (DOCs) Hom N. Sharma, Steven L. Suib, and Ashish B. Mhadeshwar Part V: Applications Hydrodesulfurization 6. Hydrodesulfurization Studies on SBA-16 Supported Molybdenum Hydrotreating Catalysts Kapil Soni, Thallada Bhaskar, Manoj Kumar, Kamaraju Seetha Rama Rao, and Gudimella Murali Dhar Epoxidation 7. Characterization and Catalytic activity of Cu-TUD-1 for Styrene Epoxidation Muthusamy Poomalai Pachamuthu, Anand Ramanathan, Kannan Santhi, and Rajamanickam Maheswari 8. Rapid Room Temperature Synthesis of Ce-MCM-48: An Active Catalyst for trans-Stilbene Epoxidation with tert-Butyl Hydroperoxide Anand Ramanathan, Rajamanickam Maheswari, Prem S. Thapa, and Bala Subramaniam Syngas Conversion 9. Rhodium Nanoparticles Confined in Ordered Mesoporous Carbon: Microscopic Characterization and Catalytic Application for Synthesis Gas Conversion to Ethanol Song-Hai Chai, Jane Y. Howe, Michelle Kidder, Xiqing Wang, Viviane Schwartz, Steven H. Overbury, Sheng Dai, and De-en Jiang Dehydrogenation 10. Carbon-Mediated Catalysis: Oxidative Dehydrogenation on Graphitic Carbon Viviane Schwartz, Steven H. Overbury, and Chengdu Liang Emerging Areas ? Renewables Conversion 11. Supported Hybrid Enzyme-Organocatalysts for Upgrading the Carbon Content of Alcohols Kapil Kandel, Stacey M. Althaus, Marek Pruski, and Igor I. Slowing 12. Activity and Selectivity of Base Promoted Mono and Bimetallic Catalysts for Hydrogenolysis of Xylitol and Sorbitol Xin Jin, Bala Subramaniam, and Raghunath V. Chaudhari 13. The Effect of Calcination Temperature on the Properties and Hydrodeoxygenation Activity of Ni2P Catalysts Prepared Using Citric Acid Victoria M. L. Whiffen and Kevin J. Smith 14. Hydrocarbon Production from Carboxylic Acids via Catalytic Deoxygenation: Required Catalytic Properties Zhong He and Xianqin Wang Editors' Biographies Indexes Author Index Subject Index

We report herein a facile synthesis of fullerene-like cages, which can be opened and closed through simple thermal treatments. A glassy carbon with enclosed fullerene-like cages of 2-3 nm was synthesized through a soft-template approach that created open mesopores of 7 nm. The open mesopores provided access to the fullerene-like cages, which were opened and closed through heat treatments in air and inert gas at various temperatures. Catalytic measurements showed that the open cages displayed strikingly higher activity for the oxidative dehydrogenation of isobutane in comparison to the closed ones. We anticipate that this synthesis approach could unravel an avenue for pursuing fundamental understanding of the unique catalytic properties of graphitic carbon nanostructures.

Nanosized anatase (or = 10 nm), rutile (or = 10 nm), and brookite (approximately 70 nm) titania particles have been successfully synthesized via sonication and hydrothermal methods. Gold was deposited with high dispersion onto the surfaces of anatase, rutile, brookite, and commercial titania (P25) supports through a deposition-precipitation (D-P) process. All catalysts were exposed to an identical sequence of treatment and measurements of catalytic CO oxidation activity. The as-synthesized catalysts have high activity with concomitant Au reduction upon exposure to the reactant stream. Mild reduction at 423 K produces comparably high activity catalysts for every support. Deactivation of the four catalysts was observed following a sequence of treatments at temperatures up to 573 K. The brookite-supported gold catalyst sustains the highest catalytic activity after all treatments. XRD and TEM results indicate that the gold particles supported on brookite are smaller than those on the other supports following the reaction and pretreatment sequences.

The overall objectives of this project are to explore the potential of novel monometallic and bimetallic Mo-based carbide catalysts for heavy hydrocarbon coprocessing, and to understand the fundamental chemistry related to the reaction pathways of coprocessing and the role of the catalysts in the conversion of heavy hydrocarbon resources into liquid fuels based on the model compound reactions.

Comparison of the hydrodenitrogenation rate of a series of isomeric amines was performed over Mo2C, NbC, NbMo2−O−C and MoS2/SiO2 catalysts. It is shown that the reaction occurs mainly through an elimination mechanism and that the order of reactivity does not correlate with the surface acidity of the catalysts.