This research developed new forms of photocatalysts that could potentially move photocatalytic degradation of air contaminants into the main stream of industrially used remediation technologies. Tests of the photocatalytic activity of the TiO2 aerogel catalysts have been carried out using both acetone and methane as the air contaminant. For comparison, the same tests were carried out on a standard (non-aerogel) anatase powder. Despite having very low crystallinity, the aerogel decontaminates the air far more effectively than an equal volume of the anatase powder which indicates that a much larger fraction of the aerogel is activated by the UV light. Experimental data were used to determine adsorption equilibrium constants for acetone, and to determine reaction rate constants assuming a Langmuir-Hinshelwood type rate expression.

After mentioning the need for integration of the catalyst and the catalytic reactor, it is argued that thin (thickness up to about 50 μm) porous layers applied on ceramic or metallic surfaces are presenting interesting possibilities for the development of new catalytic reactors. The first type of reactions that can benefit from the new reactors are liquid-phase reactions catalyzed by a solid. Especially the selectivity of the reactions can be significantly improved. The second type of reactions are gas-phase reactions with a large thermal effect. It is argued that the rate of transport of thermal energy can be greatly improved by using sintered metal bodies within the reactor coated with highly porous ceramic layers. Finally utilization of thin ceramic porous layers in separations combined with catalytic reactions is shortly dealt with.

A very efficient procedure for application of the porous ceramic layers is presented, viz., pyro-lysis of thin layer of silicone rubber or analogous compounds. Addition of, e.g., aluminum or titanium ions can be used to control the thermostability and the pore-size distribution of the layers resulting after combustion of the organic constituents.

The crystal orientation of a submicron silicalite membrane is examined using standard x-ray diffraction and pole-figure analyses. Results indicate that the crystals in the molecular sieving layer are preferentially oriented with both straight and sinusoidal channel networks of the zeolite parallel to the membrane surface. This requires that transport across the membrane proceed down the c-axis of the crystals which can occur by jumping between the two channel networks. EDAX data confirms that the molecular sieving layer is the pure silica zeolite silicalite.

Carboxylato-alumoxanes are aluminum-oxygen macromolecules consisting of a boehmite-like core surrounded by a sheath of carboxylate groups. The alumoxanes may be processed like organic polymers yet when fired are readily transformed into ceramic oxides. The alumoxanes can be precisely doped at room temperature in aqueous solution with a range of metal cations to prepare novel catalyst and catalyst support materials. The ease of introduction of multiple cations into the alumina lattice via the alumoxane approach provides a method for fine-tuning catalyst support properties and the fabrication of new catalyst materials themselves. Manganese-doped alumina (Mn-Al2O3), formed via the doping of an alumoxane with Mn at room temperature, is presented as an example where the alumoxane route provides enhanced catalytic performance over traditional approaches for the low temperature catalytic oxidation of chlorinated hydrocarbons (CHCs). The Mn-Al2O3 formed from the Mn-doped alumoxane is compared with MnO2/Al2O3 prepared by the incipient wetness method, and commercial Pt/Al2O3 for the oxidation/destruction of dichloromethane (CH2Cl2).

A novel series of photocatalysts for an overall water splitting is reported. The catalysts have a layered perovskite type structure with a general formula of A2−xLa2Ti3−xNbxO10 (A = K, Rb, Cs; x = 0, 0.5, 1.0). The catalysts, except for the one with x=1.0, are spontaneously hydrated, and the band gap irradiation induced efficient evolution of H2 and O2 in a stoichiometric ratio from an aqueous alkaline solution when a proper amount of Ni loading was made. The reaction mechanism of water splitting on these catalysts is discussed on the bases of the structural study of the catalysts.

The prototype expert system ESYCAD (expert system for catalyst design) was set up for assisting in the design of heterogeneous catalysts. It selects materials as catalyst components which have all required properties for the various (elementary) steps of a target reaction but which do not catalyze undesired side reactions. If necessary, also secondary catalytic components or promoters are selected; furthermore, reaction conditions are proposed if required by catalyst properties. The application of the system is illustrated by examples for CO-hydrogenation, alkane dehydrogenation, and for oxidative coupling of methane.

Bulk and surface properties of dispersed partially stabilized zirconias (PSZ) prepared via coprecipitation of zirconium and alkaline-earth metal hydroxides have been studied by XPD, SIMS, IR spectroscopy of surface hydroxyls and adsorbed C.O. For Sr- and Ca-PSZ, the number of the Lewis acid centers, surface concentration of the guest cation and Zr-O bonding strength at the surface have been found to deviate substantially from the values predicted by a bulk truncation model, while for Ba-PSZ it seems to be valid. A local reconstruction of the near-surface layer into the perovskite-like structure was proposed for the first two systems, which explained satisfactorily their surface properties including catalytic performance in the selective reduction of nitrogen oxides by propane in the excess of oxygen. Such reconstruction is probably facilitated by segregation of the guest cations in the subsurface layer. The driving force for this process depends upon site preference of the alkaline-earth cations to cubooctahedrons and steric factors.

In recent years the cost of research is increasingly dear to the sponsoring organizations, whether we speak of the public or private sector. Yet to meet the demand to make advances in product-generating technologies and to do so with slimmer margins, cost savings have to be developed along the chain of process events needed for production. In addition, the public atlarge has voiced their mandate for more environmentally benign operations. One look at the program for the 5th World Congress of Chemical Engineering (San Diego, 1996) would quickly show this trend. Both of the above-mentioned concerns merge together in the world of the chemical producer, generating a call for breakthroughs in the synergy of combining advanced catalytic materials with novel engineering processes. Thus, catalysis remains a focal point for technological progress [1].

Zeolites continue to be used as advanced catalytic materials, their contribution of molecular size discrimination, potential stability and high activity highlighting them as candidates for use in developing new process chemistry. Production of alkyl aromatics has seen recent trends in the replacement of existing corrosive catalyst technology by the safer solid acid zeolite catalysts [2]. The lube oil business has experienced the introduction of new Isodewaxing catalysts, capable of producing higher yields of desired product, and thereby reducing waste loss in the overall process scheme [3].

Our work on the preparation of zeolite ship-in-a-bottle complexes, which involves the encapsulation of metal complexes during zeolite synthesis, encouraged us to explore the relatively unknown structure directing properties of metal complexes. In particular, we have shown that bis(pentamethylcyclopentadienyl) cobalt(III) hydroxide, Cp*2CoOH was a template for the novel high silica zeolite UTD-1 which is the first zeolite having greater than a 12 membered ring pore structure. We have extended this strategy to other oxide compositions and metal complexes. In this paper we describe the preparation and characterization (XRD, SEM) of the gallophosphates Cloverite and UTD-10 using the metal complex [Co(NMe3)2sar]5+ (where (NMe3)2sar = 1,8-bis(trimethylammonio)-3,6,10,13,16,19-hexaazabicyclo[6.6.6]-icosane) as the template.

Aerogels are a class of colloidal materials which have high surface areas and abundant mesoporous structure. SiO2 aerogels show unique physical, optical and structural properties. When catalytic metals are incorporated in the aerogel framework, the potential exists for new and very effective catalysts for industrial processes. Three applications of these metal-containing SiO2 aerogels as catalysts are briefly reviewed in this paper — NOx reduction, volatile organic compound destruction, and partial oxidation of methane.

Hydrotalcites are mineral anion exchangers whose exchange capacity is determined by the amount of structural magnesium atoms (octahedrally coordinated) substituted by aluminium atoms. In this work we study the synthesis of hydrotalcites using a domestic microwave oven at room pressure. The effect of the oven power on the composition and on the resulting structure of two hydrotalcites differing on their nominal Al/Al+Mg ratio is presented.

Microraman and scanning electron microscopy studies have been performed on pure TiO2 and Nb-Ti-O nanopowders obtained by laser induced synthesis. The effect of Nb content on the temperature of the anatase to rutile phase transformation, induced by annealing in air at different temperatures, has been evidenced and related to the changes in the particle size distributions obtained from a Fourier analysis of the X-ray diffraction patterns.

A series of nanostructured, highly defective, ternary solid solutions containing CeO2, ZrO2, and MnO2 or CuO were prepared by high-energy mechanical milling of individual components. Morphological and redox properties were studied by XRD, HRTEM and temperature-programmed reduction techniques. It was shown that the introduction of small amounts of copper and manganese strongly promotes the redox behavior of cerium at lower temperatures in comparison with CeO2 and CeO2-ZrO2. High temperature treatment of up to 1400K was also shown to further promote overall redox capacity without affecting low-temperature redox behavior. Moreover, evidence is provided to show that Cu and Mn are dissolved within the CeO2 lattice structure. Addition of dopants enhances catalytic redox properties in the oxidation of CO at low temperatures, which is associated with the high concentration of oxygen vacancies that form on the introduction of aliovalent elements into the ceria-zirconia lattice.

The versatility of heteropolyanions implies many different uses for Keggin type catalysts. However, new roles for these catalysts must first be preceeded by further understanding of the mechanisms by which they operate. It has been observed that the solvation and/or complexation of heteropolyanions promotes or limits activity in homogeneous chemistry. For this reason the solution state and the solvation characteristics of the catalyst were studied in oxidation and photochemical reactions. Simple oxidation reactions provide a system by which the solution state of the catalyst can be studied. The catalyst used for these mechanistic studies is the Keggin ion (PMo10V2O40)−5.

This paper suggests that materials science is an important driver for innovation in applied catalysis. A wide range of catalytic materials is discussed in support of this thesis, with porosity as a common theme, and covering micro, meso and macro-porous materials. Applications of these materials is also wide-ranging, covering processes for the manufacture of fine chemicals or petrochemicals, and in oil refining, natural gas conversion and environmental processes. Further im-provents in the rate of innovation can be expected from new partnerships which are being formed, both at business and research levels.

To meet the increasingly strict automobile emissions requirements for conventional vehicles, considerable improvements in catalyst technology are required. It is now recognized that a primary challenge in meeting the ultra-low emissions vehicle standards (ULEV) for automobiles is in reducing cold-start emissions, and this generally requires a catalytic converter that has a rapid temperature response. Conventional converters (typically made from ceramic or metal monoliths) have a relatively slow temperature response due to their high thermal mass and limited heat transfer characteristics. We present details of a novel catalyst technology (Microlith™) that offers considerable advantages for this application because of greatly enhanced heat and mass transfer characteristics. Results of performance tests are also presented that demonstrate this catalyst's effectiveness. The effects of thermal aging on microstructure and catalyst performance are also discussed.

Exhaust gas heat is the primary source of warming in a conventional automotive exhaust catalyst. It typically becomes operational within minutes after the initial start-up of an engine, when it attains temperatures greater than approximately 350°C. However, around 70% of the total hydrocarbon and carbon monoxide (CO) emissions of a modern gasoline powered vehicle, under a normal driving cycle, are released during this period of cold-start. One of the strategies suggested to treat the pollutants during the first minute after initial start-up involves electrically heating the catalyst. However, devices developed for this purpose are power intensive, can require a second battery and can reduce fuel economy. The increased weight, in turn, results in increased pollution. Here we describe a low power consumption prototype which contains a conducting layer beneath the washcoat. The prototype [4 cm2] was tested at a gas flow rate of 100 seem and required less than 5 Watts to attain temperatures greater than 350°C in less than 10 seconds. The prototype was tested in a flow reactor and found to rapidly heat up to light-off temperatures where the conversion of the hydrocarbons and CO takes place. We also summarize progress made in our laboratory in the fabrication of a test device employing sol-gel processed metal oxide films.

The direct decomposition of NO (2NO → N2+02) has been carried out using an electrochemical membrane reactor composed of an yttria-stabilized zirconia (YSZ) disc deposited with Pd and Au metal films at reaction temperature of 773∼1023 K and applying voltage of 0∼1.8 V. N2 and O2 were continuously produced in the cathode and anode chambers, respectively. NO decomposition activity increased by applying electrical potential. It was clearly shown that the enhancement of the catalytic activity was due to electrochemical pumping, by which the surface oxygen species formed by the dissociation of NO were transported from cathode to anode through YSZ. By comparing the catalytic activity between Pd/YSZ/Au and Au/YSZ/Au systems, it is suggested that the NO decomposition occurs mainly on the Pd surface, and YSZ itself did not catalyze the reaction at lower temperature. The rate-determining step for the reaction was the adsorption of NO at 973 K, while at 773 K, the step was either a diffusion of O2- in YSZ or a migration of surface oxygen species on the Pd surface. The surface observation of Pd films by SEM showed that many microvoids were created throughout the Pd surface after the reaction. The creation of the microvoids results in an increase in the number of three-phase boundary sites, which will play an important role for the enhancement of the NO decomposition. Moreover, it was found that Pd/YSZ/Au resisted a serious degradation of the activity in the presence of O2 in the feed stream.

Development of new NOx sensors, which would be sensitive, selective, inexpensive and stable at elevated temperature, will greatly contribute to the reduction of the air pollution. In this paper, synthesis and performance of zeolite film applied for gas sensing are reported.

Zeolite thin films (Cu ion-exchanged ZSM-5) were synthesized on the gold electrode of AT-cut quartz platelet by hydrothermal synthesis. In order to probe the target molecule (NO) selectively, Na in as synthesized ZSM-5 film was ion-exchanged with Cu. The films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The synthesis condition for orientation to (0×0) face, on which the straight pores of ZSM-5 are opening, was optimized.

The bulk type quartz oscillator coated with Cu-ZSM-5 thin layer was tested as NO sensor in a flowing stream of He. This sensing system could be operated at high temperature because of the thermal stability of the ZSM-5 film and the gold electrode. As a result, NO was successfully detected at 348 K.