Catalytic Support Material Research Articles

Support-shape dependent catalytic activity in Pt/alumina systems using ultra-small (USANS) and small angle neutron scattering (SANS)

The correlation between the morphology of catalyst supports and their effect on catalyst dispersion was investigated. The structure of two types of γ-alumina (γ-Al2O3) crystallite particles, rod-like and platelet-like alumina, were measured in 4 orders of length scales, from nanometer to micrometer, using ultra small angle neutron scattering (USANS) and SANS and quantitatively characterized with Hammouda's Generalized Guinier–Porod model. Pt nanoparticles tended to deposit in finer particles and had narrower particle size distribution on the rod-like alumina supports compared to the plate-like alumina supports due to geometrically restricted deposition areas and higher surface curvatures of the rod-like supports. The high diffusion barrier for Pt particles on the highly curved surfaces of the rod-like supports was attributed to be the reason why Pt particles were prevented from diffusing and clustering. While aggregates of the rod-like alumina supports were randomly dispersed without any specific orientation, resulting in high surface area, aggregates of the plate-like alumina supports consisted of a stack of 2–3 layers due to the high van der Waals forces between planar layers, resulting in low surface area. Pt/rod-like alumina supports showed more than 100% higher catalytic activities than Pt/platelet-like alumina supports in model three-way-catalyst (TWC) reactions of CO, NO, and C3H6 conversions at 200–250°C. Control of shape and aggregation of catalytic support materials in nano–micrometer scale can be an important parameter to improve catalytic performance.

Synthesis of meso- and macro- porous aluminosilicate over micro-channel plate as support material for production of hydrogen by water-gas shift (WGS)

Meso- and macro-porous aluminosilicate was synthesized using a templating method. Aluminosilicate, which consists of alumina and silica, is a zeolite ceramic that exhibits high porosity and high specific surface area. These properties make aluminosilicates good catalytic support materials. Despite this, the applications of aluminosilicates have been limited to the catalytic conversion of light gases because of the small pore size, < 2 nm. Therefore, meso- and macro-porous zeolite was synthesized for use in the catalytic process for the large size molecules and water vapor. In this study, a range of surfactants were used to produce meso-pores, 2–5 nm in size. Polymer nano-beads were also used as a template for the formation of macro-pores in aluminosilicate. The meso- and macroporous aluminosilicate was coated over a micro-channel plate, and the coated micro-channel plates were stacked for use as a catalytic micro-channel reactor. The meso- and macro-porous aluminosilicate over the micro-channel plate was supported with copper and zinc oxide using the impregnation method for the production of hydrogen via the water-gas shift reaction.

ChemInform Abstract: SnO2: A Comprehensive Review on Structures and Gas Sensors

AbstractReview: 886 refs.

Ionic Liquids in Catalysis

Ionic liquids (ILs), salts with melting points below 100 °C, represent a fascinating class of liquid materials typically characterized by an extremely low vapor pressure. Besides their application as new solvents or as electrolytes for electrochemical purposes, there are two important concepts of using ILs in catalysis: Liquid–liquid biphasic catalysis and IL thin film catalysis. Liquid–liquid biphasic catalysis enables either a very efficient manner to apply catalytic ILs, e.g. in Friedel–Crafts reactions, or to apply ionic transition metal catalyst solutions. In both cases, phase separation after reaction allows an easy separation of reaction products and catalyst re-use. One problem of liquid–liquid biphasic catalysis is mass transfer limitation. If the chemical reaction is much faster than the liquid–liquid mass transfer the latter limits the overall reaction rate. This problem is overcome in IL thin film catalysis where diffusion pathways and thus the characteristic time of diffusion are short. Here, Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL) are the two most important concepts. In both, a high surface area solid substrate is covered with a thin IL film, which contains either a homogeneously dissolved transition metal complex for SILP, or which modifies catalytically active surface sites at the support for SCILL. In each concept, interface phenomena play a very important role: These may concern the interface of an IL phase with an organic phase in the case of liquid–liquid biphasic catalysis. For IL thin film catalysis, the interfaces of the IL with the gas phase and with catalytic nanoparticles and/or support materials are of critical importance. It has recently been demonstrated that these interfaces and also the bulk of ILs can be investigated in great detail using surface science studies, which greatly contributed to the fundamental understanding of the catalytic properties of ILs and supported IL materials. Exemplary results concerning the IL/vacuum or IL/gas interface, the solubility and surface enrichment of dissolved metal complexes, the IL/support interface and the in situ monitoring of chemical reactions in ILs are presented. Important concepts in catalysis with ionic liquids are reviewed, including Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL), along with the detailed analysis of the relevant interfaces using surface science methods.

ChemInform Abstract: Recent Advances of Doping of SnO2 Nanocrystals for Their Potential Applications

AbstractReview: 88 refs.

Accurate amorphous silica surface models from first-principles thermodynamics of surface dehydroxylation.

Accurate atomically detailed models of amorphous materials have been elusive to-date due to limitations in both experimental data and computational methods. We present an approach for constructing atomistic models of amorphous silica surfaces encountered in many industrial applications (such as catalytic support materials). We have used a combination of classical molecular modeling and density functional theory calculations to develop models having predictive capabilities. Our approach provides accurate surface models for a range of temperatures as measured by the thermodynamics of surface dehydroxylation. We find that a surprisingly small model of an amorphous silica surface can accurately represent the physics and chemistry of real surfaces as demonstrated by direct experimental validation using macroscopic measurements of the silanol number and type as a function of temperature. Beyond accurately predicting the experimentally observed trends in silanol numbers and types, the model also allows new insights into the dehydroxylation of amorphous silica surfaces. Our formalism is transferrable and provides an approach to generating accurate models of other amorphous materials.

Recent Advances of Doping of SnO2 Nanocrystals for Their Potential Applications

SnO2 nanocrystal is a novel wide band gap n-type semiconductor which exhibits outstanding electrical, optical and electrochemical properties that can be exploited for solar cells, catalytic support materials, transparent electrodes and solid-state chemical sensors applications. The main focus of this article is to address the impacts of doping on the various properties of SnO2 nanocrystals including optical, electrical, photocatalytic and gas sensing. Recently, emphasis is given on metal ion doped SnO2 nanocrystals to enhance the electrical and optical properties. Metal ion doped SnO2 nanocrystals are found to be potential candidates for gas-sensing devices. We will begin with the description of general synthetic methodologies for designing doped SnO2 nanostructure materials. Interesting findings are that the application-based properties such as photocatalytic and gas sensing are increased manifold after doping of SnO2 nanocrystals. Finally, a tentative outlook on future developments of this research field is given.

Hydroxyapatite supported cobalt catalysts for hydrogen generation

The controlled generation of H2 from storage materials by using an efficient catalytic support is a highly sought after technology; however, the majority of successes utilize expensive materials considered unfeasible. In our report on the creation of a novel, durable, and inexpensive catalytic support material for hydrogen generation, we examine a critical surface modification of hydroxyapatite (HAP) with cobalt ions to provide the necessary catalytic transition metal for the fast hydrolysis of the hydrogen storage material, sodium borohydride (NaBH4). By altering the morphology and composition of the HAP crystal supports, we revealed novel methods for enhancing the hydrogen generation rates. Particularly, lowering the Ca composition during synthesis of the HAP crystals afforded a Ca deficient HAP capable of exhibiting a higher surface coverage of cobalt, thereby eliciting faster hydrolysis reaction rates in comparison with the amorphous HAP control having the characteristic Ca content for HAP. A more significant increase in hydrogen generation was observed when using single crystal HAP in comparison with amorphous and calcium deficient HAP supports. Despite the smaller surface area of the hydrothermally prepared single crystal HAP, it provided significantly faster hydrogen generation. Each of the HAP supports exhibit repeatability with catalytic efficiency decreasing by approximately 25% over 3weeks upon repeated daily exposure to solutions of the hydrogen storage material NaBH4. Through these experiments, we proved that altering the composition and morphology of cobalt ion exchanged HAP supports can offers a useful means for increasing the rate of controlled hydrogen generation.

Novel application of cotton stalk as a waste derived catalyst in the low temperature SCR-deNOx process

The use of activated carbon derived from cotton stalk as a potential catalytic support material in the application of NO removal from coal combusted flue gas was experimentally investigated utilizing the SCR-deNOx process. Cotton stalk samples infused with phosphoric acid were chemically activated (CACS) and co-activated (CO-ACS) and impregnated with the metal configuration Mn/Ce (1:2M ratio) representing 4wt.% relative to the support material. The CACSx–Mn/Ce and CO-ACSx–Mn/Ce catalysts provided NO conversion efficiencies ranging between ∼10% and 68%. The addition of phosphoric acid significantly increased the BET surface area (m2g−1) of the respective CACSx–Mn/Ce and CO-ACSx–Mn/Ce catalysts. However based on the experimental and analytical findings this study suggests that the NO conversions efficiencies of the CACSx–Mn/Ce and CO-ACSx–Mn/Ce catalysts are far more dependent on the wt.% of the metal loading than the physical parameters such as the pore size, pore structure and surface area. The relatively lower NO conversion efficiencies may also be further due to the neutralization of the Lewis and Brönsted acid sites of the catalysts by the presence of any alkali metals within the cotton stalk. The cotton stalk derived catalytic support has shown a great potential for possible application within the SCR-deNOx process. It is further suggested that higher NO conversion efficiencies can be realized by an increase in the metal loadings of Mn/Ce for the CACSx–Mn/Ce and CO-ACSx–Mn/Ce catalysts.

Carbon Nanotubes: A Promising Catalyst Support Material for Supercritical Water Gasification of Biomass Waste

AbstractSupercritical water (SCW) as a reaction medium is especially promising for the production of renewable chemicals from biomass. Stability issues of catalyst support materials in SCW are a major setback for these reactions and hinder the further development and industrial exploitation of this technique. The development of stable catalytic support materials for reactions in SCW is, therefore, of great importance. Carbon nanotubes (CNTs) are widely recognized for their significant physical and chemical stability, high heat conductivity, and open structure. These properties have already been explored for different applications. We show that CNTs are a promising stable catalyst support material for reactions in SCW. As an illustration of the applicability of CNTs in SCW, we demonstrate the efficiency of Pt‐CNTs as catalysts for the production of hydrogen by reforming of ethylene glycol and acetic acid in SCW.

Surface hydroxyl concentration on Zr(OH) 4 quantified by 1H MAS NMR

Zirconium hydroxide (Zr(OH) 4) is a catalytic support material whose reactivity depends on intrinsic surface hydroxyl groups. Here we present a 1H MAS NMR study where we identify bridging and terminal hydroxyl groups along with their concentrations even in completely dehydrated material. The dehydrated material contains 13 mmol/g bridging hydroxyl groups and 3.9 mmol/g terminal hydroxyl groups, yielding a ratio of 3.4:1, and is verified by XPS. Upon hydration, the number of surface hydroxyl groups remains constant while only bulk water is adsorbed on the surface. Knowing both the types and amounts of surface hydroxyl groups on Zr(OH) 4 helps explain the catalytic activity of Zr(OH) 4 in many applications.

Surface modification of hydroxyapatite for hydrogen generation

Hydrogen provides a safe and clean alternative to carbon-based fuels. Having the proper catalytic support for production of hydrogen is a valuable technology. We report on the surface modification of hydroxyapatite as a novel catalytic support material for hydrogen generation. Aside from being inexpensive and durable, we reveal that Ru ion exchange on the HAP surface provides a highly active support for sodium borohydride hydrolysis, exemplifying a high total turnover number on the order of 24,000 mol H 2/mol Ru. Moreover, we observe that the RuHAP support exhibits a long catalytic lifetime of approximately 1 month upon repeated exposure to NaBH 4 solutions. We identified the ability of complex surface morphology to enhance hydrolysis by the catalytic transition metal covered surface. Particularly, we found that the complex morphology of polycrystalline RuHAP catalytic supports exhibits shorter induction times for hydrogen generation as well as improved reaction rates as compared with single crystal supports possessing the same Ru content. By decreasing induction time and enhancing catalytic activity, we find it feasible to further explore this catalyst support in the construction of a practical hydrogen generation system.

Nanocarbon Synthesis Using Oxidized Diamond-Supported Metal Catalysts

Nanocarbons could be obtained by the decomposition of light alkanes using oxidized diamond-supported Ni catalyst with high yields. This is the report to show that oxidized diamond can serve as an active catalytic support material for nanocarbon synthesis. Oxidized diamond is proposed as a novel catalytic means for the synthesis of nanocarbons, and it is suggested that oxidized diamond may catalyze unique reactions of importance in nanomaterial synthesis.

A Feasibility Study of Wire-Woven Cellular Metal as Catalytic Support Material

Wire-woven bulk Kagome (WBK) specimens were fabricated by wires made of Fecralloy, a Fe-Cr-Al alloy, and their feasibility as supports for an oxidation catalyst was investigated. For catalytic reactivity, the catalyst-coated WBK supports perform as well as the corresponding cordierite support, even though the WBK support has much lower flow resistance. Moreover, WBK is advantageous in terms of mass productivity, weight, durability and impact strength. The image shows a close-up view of the WBK support after heat treatment.

Kinetics of reduction and oxidation reactions for application in catalytic gas–particle-filters

Catalytic filters offer the possibility to combine the functions of a catalytic reactor and a gas–particle filter within one process step. In this way, plant complexity may be reduced, which is of economical interest for small- to medium-size biomass combustion plants. SiC materials seem attractive for catalytic activation as they exhibit high heat conductivity and good thermal shock resistance properties. Furthermore, SiC filter candles are coated with a dense mullite membrane (SiO 2–Al 2O 3 coating), which protects the inner porous, catalytic filter support material against any catalyst poisons carried by the particles. Within this research, filter candles based on SiC, manufactured and impregnated with V 2O 5–TiO 2–WO 3 catalysts by Pall–Schumacher, are investigated with respect to catalytic reactions in gas cleaning. For a better kinetic analysis also accordingly catalytic impregnated SiC grains were investigated in a fixed bed reactor.

Investigation of the structure and the redox behavior of gadolinium doped ceria to select a suitable composition for use as catalyst support in the steam reforming of natural gas

Gadolinium doped cerias with a gadolinium content in the range 0≤xGd≤0.5 were synthesized using a glycine-nitrate combustion process. The resulting materials are weak agglomerates showing low specific surface area, no microporosity and are stable against sintering. While the addition of gadolinium enhances the surface reactivity and thus the dynamic oxygen exchange capacity (OEC), it depresses bulk reduction. As a result, the total oxygen storage capacity (OSC) is much lower compared to pure ceria. For small-scale hydrogen production using the steam-reforming process, these support properties are expected to be beneficial. The materials with an intermediate gadolinium content of xGd≈0.2–0.25 are determined to be especially suitable for use as catalytic support material in this application.

Cordierite-CeO&lt;sub&gt;2&lt;/sub&gt; Composite Ceramic: A Novel Catalytic Support Material for Purification of Vehicle Exhausts

Stable oxygen concentration in exhausts is a decisive factor in catalytic purification of the vehicle exhausts. Nanostructured CeO2 is generally added into catalytic coating on a ceramic support to adjust the oxygen concentration because it possesses a unique oxygen storage capacity (OSC). However, a small amount of CeO2 gets insufficient when the oxygen concentration fluctuates in a large range. In the present work, the cordierite-CeO2 composite ceramic with oxygen storage capacity was prepared for a support material of catalytic converters. The oxygen storage-release performance of the ceramics, including temperature of releasing oxygen, adsorption process of oxygen and the oxygen storage, was examined by a temperature-programmed gas chromatography. The composition of the ceramics was analyzed by an X-ray powder diffraction (XRD) and a scanning electron microscope (SEM) to validate the reliability of the ceramic as the support material with OSC. Results show that the ceramics consist of α-cordierite and CeO2 phases, the latter of which is uniformly dispersed throughout the cordierite matrix. The ceramic powder with 10-20wt% of CeO2 possesses the expected oxygen storage capacity. It is suggested that this novel cordierite-CeO2 composite ceramic is helpful of improving the purification effect of vehicle exhausts.

Supercritical fluids: A route to palladium-aerogel nanocomposites

Supercritical carbon dioxide (scCO2) is used to prepare novel silica aerogel composites containing nano-particles of palladium. The material produced has been found to exhibit a Pd loading of 8% by wt. The particles deposited fit within two discrete size ranges of <6 nm and 15–20 nm as analysed by XRD and TEM. We demonstrate that scCO2 may be successfully applied to prepare catalytic support materials based upon aerogels and that the catalyst is active in a continuous flow reactor leading to effective hydrogenation of cyclohexene.

Novel Selective Oxidation of Light Alkanes Using Carbon Dioxide. Oxidized Diamond as a Novel Catalytic Medium.

Carbon dioxide is an effective oxidant for the conversion of alkanes to chemical feedstocks. Oxidized diamond is useful as a novel catalytic support material. Oxidized diamond provided catalytic sites for the activation of alkanes under CO2 atmosphere. The present findings also suggest that the surface-properties of oxidized diamond may facilitate unique catalytic reactions, such as alkanes conversion in the presence of CO2.

Novel Selective Oxidation of Light Alkanes Using Carbon Dioxide. Oxidized Diamond as a Novel Catalytic Medium

Abstract Carbon dioxide is an effective oxidant for the conversion of alkanes to chemical feedstocks. Oxidized diamond is useful as a novel catalytic support material. Oxidized diamond provided catalytic sites for the activation of alkanes under CO2 atmosphere. The present findings also suggest that the surface-properties of oxidized diamond may facilitate unique catalytic reactions, such as alkanes conversion in the presence of CO2.