In this study we have used commercially available preformed sols as building blocks to systematically explore the effects of composition, particle size, and packing on the textural and acidic properties of alumina-silica. We have prepared single oxides and alumina-silica mixed oxides with varying Al:Si atomic ratios using commercial sols from Vista Chemical Co. (alumina) and Eka Chemicals, Inc. (silica). Simple particle packing models based on the structure and experimentally determined particle size distributions of the sols explain the textural and acidic properties of both the single and mixed oxides. Comparisons with aerogels prepared from alkoxides show that materials with different atomic-scale homogeneity can be obtained. This continuum of precursor sizes from monomer through colloid allows a measure of control over textural and acidic properties in the mixed oxides, even at a fixed composition. These results show that systematic studies using preformed sols add insight into the effect of preparation upon catalytic materials.

The gels derived from mixtures of Pr(OiC3H7)3 and Zr(OiC3H7)4•iC3H7OH, upon hydrolysis and pyrolysis, furnish single-phase PrOy-ZrO2 materials crystallized in the fluorite structure. These materials can be coated onto high-surface-area γ-alumina powders or deposited onto dense α-alumina coupons in the form of thin films from a solution of parent alkoxides modified with 2,4-pentanedione in THF. The fluorite structure of the PrOy-ZrO2 in the films appears to be thermally stable in air up to 1200°C. Temperature-programmed-reduction (TPR) measurements show that the bulk PrOy-ZrO2 material with a Pr. Zr molar ratio of 1:1 can store and release oxygen while that with a molar ratio of 1:3 cannot.

The precursors play an important role in determining phase composition of the resulting PrOy-ZrO2 material. A mixture of monoclinic and cubic or tetragonal phases was found in PrOy-ZrO2 prepared from a new single-source heterometallic alkoxide, Pr2Zr6(μ4-O)2(μ-OAc)6(μ-OiPr)10(OiPr)10, whereas a mixture of cubic and tetragonal phases was present in PrOy-ZrO2 made previously by coprecipitation from aqueous solutions of the metal nitrates.

The oxidative dehydrogenation (ODH) reactions for the formation of two important organic feedstocks ethylene and propylene are of great interest because of the potential in capital and energy savings associated with these reactions. Theoretically, ODH can achieve high conversions of the starting materials (ethane and propane) at lower temperatures than conventional dehydrogenation reactions. The important focus in our study of ODH catalysts is the development of a structure-property relationship for catalyst with respect to selectivity, so as to avoid the more thermodynamically favorable combustion reaction. Catalysts for the ODH reaction generally consist of mixed metal oxides. Since for the most selective catalyst lattice oxygen is known to participate in the reaction, catalysts are sought with surface oxygen atoms that are labile enough to perform dehydrogenation, but not so plentiful or weakly bound as to promote complete combustion. Also, catalysts must be able to replenish surface oxygen by transport from the bulk.

Perovskite materials are candidates to fulfill these requirements. We are studying BaCeO3 perovskites doped with elements such as Ca, Mg, and Sr. During the ODH of the alkanes at high temperatures, the perovskite structure is not retained and a mixture of carbonates and oxides is formed, as revealed by XRD. While the Ca doped materials showed enhanced total combustion activity below 600°C, they only showed enhanced alkene production at 700°C. Bulk structural and surface changes, as monitored by powder X-ray diffraction, and X-ray photoelectron spectroscopy are being correlated with activity in order to understand the factors affecting catalyst performance, and to modify catalyst formulations to improve conversion and selectivity.

Methane conversion to synthesis gas in membrane reactors that use dense mixed electronic-ionic conducting membranes for oxygen separation has received much recent attention. The oxygen flux achievable in these reactors depends on a combination of the bulk diffusion rate for oxygen transport and the surface reaction rate for oxygen activation and either recombination or reaction with methane. Here we compare recent oxygen permeation data for tubular membranes of La0.5Sr0.5Fe0.8Ga0.2O3-δ with our previous results for SrCO0.8Fe0.2O3-δ, SrFeCO0.5O3.25-δ. The pressure dependence of the oxygen permeation flux has been measured at different temperatures and used to determine the relative importance of bulk and surface kinetics for these oxides.

Nanocrystalline and polycrystalline ZrO2, CeO2 and Mn3O4 without and with 5 wt% Pd have been tested for methane oxidation. The nanocrystalline catalysts perform better than the polycrystalline catalysts on a weight basis. Nanocrystalline (n)-CeO2 performs much better than n-ZrO2, and both perform much better than polycrystalline (P)-CeO2 and P-ZrO2. 5 wt% Pd/n-ZrO2 is the best catalyst tested, but 5 wt% Pd/n-CeO2 performs nearly as well. A 20 wt% Ag/p-ZrO2 and a 20 wt% Ag/n-ZrO2 catalyst were also tested. The Ag yields a significant improvement over the bare supports, but not as much so as Pd.

X-ray absorption near-edge spectroscopy (XANES) was used to characterize the structural and electronic properties of a series of cobalt- and nickel-molybdate catalysts (AMoO4.nH20, α-AMoO4, β-AMoO4; A= Co or Ni). The results of XANES indicate that the Co and Ni atoms are in octahedral sites in all these compounds, while the coordination of Mo varies from octahedral in the a-phases to tetrahedral in the β-phases and hydrate. Time-resolved x-ray diffraction shows a direct transformation of the hydrates into the β-AMoO4 compounds (following a kinetics of first order) at temperatures between 200 and 350 °C. This is facilitated by the similarities that the AMoO4.nH20 and β-AMoO4 compounds have in their structural and electronic properties. The molybdates react with H 2 at temperatures between 400 and 600 °C, forming gaseous water and oxides in which the oxidation state of Co and Ni remains +2 while that of Mo is reduced to +5 or +4. After exposing α-NiMoO4 and P-NiMoO4 to H2S, both metals get sulfided and a NiMoSx phase is formed. For the β phase of NiMoO4 the sulfidation of Mo is more extensive than for the a phase, making the former a better precursor for catalysts of hydrodesulfurization reactions.

Nonstoichiometric nickel manganite spinels NixMn3-x □3δ/4O4+δ, have been synthesised by calcination of mixed oxalates in air at 350°C. The variation of the electrical conductivity σ with partial pressure of O2 shows that these oxides are n-type semiconductors; σ also varies with the nickel content and has a maximum at x = 0.6. The intrinsic catalytic activity of these oxides for CO/CO2 conversion varies with nickel content and the most active catalyst is at x=0.6 where the conversion starts at room temperature. The variation of the catalytic activity and the electrical conductivity and the nickel amount are correlated. Apparent activation energies are very low (less than 20 kJ/mol) and remain the same for all these mixed oxides. Similarly, the reaction order with respect to O2 and CO does not depend on the nickel content (order/O2 ≈ 0; order/CO ≈ 0.6). A reaction mechanism involving formation of oxygen ions adsorbed and carbonate species is discussed.

Atomic force microscopy has been used to determine how MoO3(010) surfaces with controlled defect populations evolve during reactions with MeOH/N2 mixtures. The structural evolution of the freshly cleaved surface is compared to surfaces reduced in 10%H2/N2 at 400 °C. While the freshly cleaved surfaces are flat and nearly ideal, the reduced surfaces contain voids bounded by step loops where Mo atoms in reduced coordination are found. In both cases, reacting the MoO3(010) surface with MeOH/N2 mixtures between 300 and 400 °C leads to H intercalation and the nucleation of acicular precipitates of HxMoO3. On the freshly cleaved surface, the H-bronze phase precipitates uniformly. On the reduced surface, the precipitates form preferentially at the void edges, where undercoordinated Mo atoms are found.

It is becoming increasingly important to decompose PFCs (Perfluorocompounds), which are powerful greenhouse gases. The process of catalytic decomposition is expected to be effective in operating at lower temperatures if catalysts of high activity and durability are developed. The decomposition activities of PFC with H2O was investigated using several catalysts. It was found that PFC decomposition activity was related to the reactivity of fluorine and the formation of mixed oxides. Using the catalyst we have developed, CF4 was decomposed with conversion above 99.9% over 1988h. Furthermore, another PFC was decomposed over the catalyst. The order of the conversion was CHF3 > CF4 > C2F6. The catalytic decomposition system can use the treatment of PFCs in dry etch process waste gas.

The Ce3+ ↔ Ce4+ redox process in automotive three-way catalysts such as Ce-ZrO2/Pt provides an essential mechanism to oxygen storage/release under dynamic air-to-fuel ratio cycling. Such a function requires a metal-support interaction which is not completely understood. We have carried out an in-situ neutron powder diffraction study to monitor the crystal structures (a mixture of a major tetragonal and a minor monoclinic phase) of 10mol% Ce-doped ZrO2 with and without Pt (1wt%) impregnation under oxidizing and reducing conditions over the temperature range of 25°-700°C. The samples were heated first in flowing 2%O2/Ar from room temperature to 400°C and then in 1%CO/Ar to about 700°C. A discontinued increase of the tetragonal unit-cell volume, a decrease of tetragonality (c/a), and a change of color from light yellow to gray when changing from oxidizing to reducing atmosphere were observed only in the sample containing Pt. This result supports the model which assumes the formation of oxygen vacancies initially near the Pt atoms. As more Ce ions are reduced from 4+ to 3+ oxidation states at high temperatures, oxygen vacancies migrate to the bulk of the oxide particles.

Formation of planar layered Al2O3/Al composites via aluminum foil anodic-spark oxidation was studied by using SEM and XRD. A lateral growth of the primary non-porous alumina islands was shown to proceed to an extent where the entire surface was covered, and this layer is responsible for determining the high thermal stability of composite. A washcoating by an alumina suspension substantially increases pore volume and water absorption capacity. Catalysts based on the platinum group metals and transition metal oxides exhibit high activity for the reactions of CO and hydrocarbon oxidations and the selective reduction of nitrogen oxides by hydrocarbons.

A new kind of TiO2 film catalyst was prepared by the Plasma-enhanced chemical vapor deposition (PECVD) method. The surface photovoltaic spectroscopy (SPS) results showed that its photoresponse was extended into the visible region. Photooxidation experiments showed that this kind of TiO2 film had high photocatalytic activity on degradation of phenol in aqueous solution. The influence of the thickness of TiO2 film on its photocatalytic activity was also discussed.

An horizontal hot-wall MOCVD reactor was used to prepare palladium and platinum catalysts supported on alumina. A conventional impregnated Pt on alumina catalyst was prepared as comparison. The solids were characterized by XRD, Auger spectroscopy, HREM and H2 -TPR. The operation conditions of the MOCVD reactor were fixed preparing several Pd catalysts until to find the appropriate deposition zone. The particle size of Pt catalysts prepared by MOCVD was at about 7 nm compared with 6 ran obtained with the Pt impregnated catalyst, measured by XRD. The HREM image of the Pt MOCVD catalyst showed a narrower particle size ranging from 1 to 4 nm. After calcination three Pt compounds were detected by TPR, which were attributed to PtO, PtO2 and Pt-Al2O3 interaction in MOCVD preparation. Additionally, a clear reduction of surface oxygens of alumina was also observed.

NiZr powders produced by mechanical alloying become active NO decomposition catalysts after an activation period in reaction conditions. Although the initially glassy structure exhibits a high activity, the NiZr powder becomes temporarily inactive. After about 10 hours in reaction conditions at 673 K, the powder again becomes active with a lower, but still substantial turnover frequency for NO decomposition. Oxygen produced by the reaction appears to be consumed by the catalyst during this second period of activity.

The catalytic interaction of noble metal and main group elements in Rh/one-atomic layer GeO2/SiO2 and Pt/SbOx was investigated. The high temperature reduction produced RhGe and PtSb bimetallic particles in which Pt and Rh were electronically modified to retard catalytic activity. However, unique selective catalyses of Rh/one-atomic layer GeO2/SiO2 for CO hydrogenation reaction to oxygenate compounds and for NO+CO reaction to N2 were found. Under the low temperature reduction of Rh/one-atomic layer GeO2/SiO2 and the high temperature calcination of Pt/SbOx, the oxide phases, GeO2 and SbOx, were stable and the selective reduction of ethylacetate to ethanol and the selective oxidation of iso-C4H10 to methacrolein were observed. The high selectivities were ascribed to synergistic interaction between the noble metals and the main group element oxides through the diffusion of adsorbed species and reaction intermediates. The possibility of chemical control of noble metal-catalyses by main group elements is discussed.

We have examined supported PtRus specimens by a variety of electron microscopy techniques, including high resolution, analytical and a novel mass-spectroscopic electron microscopy techniques. Analytical electron microscopy results showed that the relative atomic concentration of Pt to Ru for each PtRu5 cluster is 1 to 5. The average diameter of the clusters was a 15.6Å, and the average number of atoms was measured to be 24 atoms per cluster. The combination of these techniques demonstrate that the PtRu5 clusters are raft-like on the carbon black support.

Present paper reports on Extended X-rays Absorption Fine Structure (EXAFS) Spectroscopy characterisation of Fe/Pt clusters. Samples of different nominal iron contents (FePt4 and FePt2) have been prepared and characterised by direct measurements of absorption coefficient at Pt L3 and Fe K edges. Catalysts were prepared by precipitation from suitable mixing (in the appropriate stoichiometry) of mesitylene suspentions containing small clusters of either platinum or iron. Single species suspention, in turn, were prepared by vapor metal deposition.

Catalitic activity of prepared samples was tested on cinnammic aldehyde. As a general result, platinum clusters exhibit activity in the hydrogenation of both carbon double bond and aldehyde group with a preference for the latter. Iron addition to the pure platinum catalyst reverts the selectivity while leaving the catalitic activity almost unchanged.

The present paper represents a temptative to achieve structural information on Fe and Pt short range environments, thus providing insights on the dynamics of the catalytic process.

The main features of porous metal/ceramic catalysts for hydrocarbons steam reforming their formation via hydrothermal treatment of the powdered aluminum and lanthanum nickelate mixture in the confined space are elucidated. For catalysts obtained via this route, their polymodal pore structure was found to approach the optimum level. The phase composition of the active component precursor was shown to have a great impact on the specific catalytic activity of catalysts.

Pt/Pd bimetallic nanoparticles were prepared by ultrasonic irradiation of aqueous solutions containing salts of both metal ions. Uniform bimetallic particles were found to have a 2.8 nm average diameter and a narrow size distribution. The size was similar to Pt monometallic particles, and the shape was similar to Pd monometallic particles, both prepared by ultrasound in the same way.

Fullerenes were found to catalyze coupling and transalkylation reactions of mesitylene, engage in transfer hydrogenations with dihydroaromatics, and cleave strong bonds such as those in diarylmethanes. In all of these reactions, fullerenes show a marked ability to accept and to transfer hydrogen atoms. The key structural feature that endows fullerenes with many of its characteristics is the presence of a pentagon surrounded by hexagons. We suspected that fullerene soot, unlike graphitic carbon, contained pentagons in a hexagonal lattice, and that these sites imparted the soot with the desired chemical attributes of strong electrophilic nature and an ability to stabilize radicals. In subsequent studies, we have shown fullerene soot to be very effective in catalyzing various H-transfer reactions, including the conversion of methane into higher hydrocarbons. When compared with other carbons, such as activated carbons and acetylene black, the fullerene soot is much more reactive for oligomerization and hydrodealkylation of alkylbenzenes. Because this activity remains, even in chemically extracted and partially oxidized soot, the observed catalysis is not a result of residual soluble fullerenes.