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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.

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 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.

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.

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.

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 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.

Nanostructured graphitic forms of carbons have shown intersting potential for catalysis research and are ideal candidates to substitute the conventional metal-oxide catalysts because they can be easily disposed, which enables a greener, more sustainable catalytic process. Few-layer graphene and its functionalized form offer the opportunity to investigate the nature of graphitic active sites for oxidation reactions in well-defined carbon-based catalysts. In this paper, we report the utilization of oxygen-functionalized few-layer graphene sheets containing variable amounts of oxygen in the heterogeneous catalytic oxidative dehydrogenation (ODH) reaction of isobutane at 400oC. Interestingly, there is poor correlation between oxygen content and catalytic performance. Carbonyl groups were found to be highly stable, and graphene that had higher sp(2) character, the lowest oxygen content, and fewer edge sites presented the lowest specific rate of isobutane reaction, although the isobutene selectivity remained high. The reoxidation of the graphene surface occurred at the same rate as the ODH reaction suggesting a Mars-van Krevelen type of mechanism, similar to that which takes place on oxide surfaces. These results appear to suggest that a higher fraction of exposed edges where oxygen active sites can be formed and exchanged should lead to more active catalysts for ODH reactions.