Ralf Zapf

Detailed Characterization of Various Porous Alumina-Based Catalyst Coatings Within Microchannels and Their Testing for Methanol Steam Reforming

A fundamental study concerning the preparation of porous alumina washcoats in microchannels for the application in heterogeneous gas phase catalysis was performed, focusing on the pre-treatment of the microstructures, properties, and adhesion of the washcoats as well as the testing of the prepared catalysts. Steel microstructures, which are manufactured by wet-chemical etching with chloride solutions, show significant chlorine content at the surface due to the etchant. Anodic oxidation and thermal treatment of the microstructures significantly reduce the undesirable chlorine content, which is assumed to have deleterious effects on the catalyst activity. Good adhesion of the porous catalysts, deposited by a two-step process, washcoating and wet impregnation, was demonstrated by a mechanical test. Cross-sectional profile accuracy was reasonable and reliable. At the example of a CuO/Cr 2 O 3 /Al 2 O 3 system, the distribution of the impregnated components within the washcoat, in lateral (depth of the coating) and horizontal directions (at the coatings surface), was studied by secondary ion mass spectrometry (SIMS). It turned out that Cr 2 O 3 was homogeneously distributed both in horizontal and lateral direction, whereas the content of CuO decreased with the washcoat depth and islands of accumulated material on the surface were formed. The activity of the CuO/Cr 2 O 3 /Al 2 O 3 system was investigated using different alumina carriers for methanol steam reforming. The activity found was correlated with the total catalyst surface area offered to the reaction system.

Low temperature catalytic combustion of propane over Pt-based catalyst with inverse opal microstructure in a microchannel reactor

A novel Pt-based catalyst with highly regular, periodic inverse opal microstructure was fabricated in a microchannel reactor, and catalytic testing revealed excellent conversion and stable activity for propane combustion at low temperatures.

A Methanol Steam Micro-Reformer for Low Power Fuel Cell Applications

Abstract A micro-reformer was fabricated and its performance investigated using copper-zinc catalysts with differing compositions and loadings at various operating conditions. A catalyst with 3:1 copper-to-zinc ratio and 8 wt% loading produced enough hydrogen to power a 28W PEM fuel cell when using a third of the reformers volume (8 cm3) and assuming 64% fuel cell efficiency. Methanol conversion was 65% while hydrogen content in the off-gas was 45% at a temperature of 275°C and residence time of 0.11s. Carbon monoxide levels were approximately 1.45%. Higher methanol conversions (80%) and hydrogen content in the off-gas (50%) were achieved by a second catalyst with 16 wt% at 290°C while utilizing the entire reformer volume. Hydrogen yield and selectivity were high (78 and 98% respectively). Extrapolating from present results, the maximum power output possible to be achieved by this device is 84 W.

Fast preparation and testing methods using a microstructured modular reactor for parallel gas phase catalyst screening

Abstract Heterogeneous gas phase catalyst screening with catalysts applied on titer-plates is presented. It will be shown that titer-plates can as well be used for the sample preparation outside the reactor and for the catalyst testing in the reactor. For the catalyst preparation, the known wash-coating-impregnation procedure is applied. An alumina coated precursor is introduced into a manifold which utilizes the flow features of the separated wells for the impregnation of the precursor with solutions of the salts of a collection of transition metals. The impregnation liquid is flowing through the wells thus impregnating the surface of the porous γ-alumina layers within the microchannels. Less porous coatings are realized by the simultaneous gradient sputtering process developed on the basis of the standard sputtering process. Some details about the reactor development and characterization as well as problems which arose are reported. For the description of the reactor performance, a number of coated titer-plates were tested and these results are presented. After this so-called primary screening, a second evaluation phase normally follows. In this second phase, the kinetic properties of a single catalyst shall be studied. For this purpose, a model which describes the fluidic behavior of the reacting gas in microchannels was developed. Applying the model will give further insights into the underlying reaction kinetic of a single selected catalyst in the so-called secondary screening phase.

Blue light mediated C–H arylation of heteroarenes using TiO2 as an immobilized photocatalyst in a continuous-flow microreactor

Titanium dioxide was applied as an immobilized photocatalyst in a microstructured falling film reactor for the continuous-flow C–H arylation of heteroarenes with aryldiazonium salts as the starting material. Detailed investigations of the catalyst and a successful long-term run proved its excellent usability for this process. Very good yields up to 99% were achieved with broad substrate scope and were compared with batch synthesis. The transfer to the continuous-flow mode revealed an impressive boost in reactor performance solely resulting from the improved irradiation and contact of the catalyst, substrate and light.

Microstructured fuel processors for fuel-cell applications

Microstructured reactors are being developed at IMM for the processing of various fuels to provide hydrogen for mobile and portable fuel-cell systems. The key feature of the systems is the integrated-plate heat-exchanger technology, which allows for thermal integration of several functions in a single device. For example, steam reforming may be coupled with exothermic reactions in separate flow-paths of a heat exchanger. Catalyst coatings are also under development for numerous reactions, such as propane steam reforming, methanol steam reforming, catalytic combustion, water-gas shift, and preferential oxidation of carbon monoxide. These catalysts are being investigated in specially developed testing reactors. Reactors and complete fuel processors are being tested up to 5 kW power output of the corresponding fuel cell.

A Novel and Miniaturised Thin Film Pellistor for Carbon Monoxide Detection in Hot Gas Flows

A thin film pellistor is under development at IMM for the selective detection of carbon monoxide in hot gas flows. The selective methanation reaction of carbon monoxide to methane is applied to generate chemical heat of reaction, which is then detected by direct measurement of thermal conductivity. The chemical reaction is performed over a nickel/calcium oxide/alumina catalyst, which is directly deposited onto a silicon nitride membrane being part of the sensor.Copyright