Jari Kiviaho

The effect of the precursor on the characteristics of Co/SiO2 catalysts

Abstract The effect of the precursor on the characteristics of the Co/SiO 2 catalysts prepared from Co(NO 3 ) 2 , Co 2 (CO) 8 and Co 4 (CO) 12 was determined. The near-surface reduction was clearly lower for the Co 2 (CO) 8 derived catalyst than for the Co 4 (CO) 12 based one. The hydrogen chemisorption, CO desorption, XRD and XPS measurements indicated that the dispersion of the metallic species decreased in the precursor order Co 2 (CO) 8 > Co 4 (CO) 12 ≫ Co(NO 3 ) 2 . The TPD studies showed that CO was more strongly adsorbed on catalysts derived from carbonyls than on those based on nitrate, resulting in greater initial activity in CO hydrogenation. In pulsed CO hydrogenation reactions, the selectivity of the Co 2 (CO) 8 derived catalyst differed from the other two. Thus, despite the well documented transformation of the Co 2 (CO) 8 to Co 4 (CO) 12 on the silica support, the supported catalysts derived from these two precursors exhibited distinct characteristics and reactivity.

Heterogeneous palladium catalysts for the Heck reaction

Abstract The vinylation of iodobenzene with methyl acrylate was studied using palladium-based heterogeneous catalysts. Methyl cinnamate was formed as vinylation product and benzene as side product. All catalysts were of the type SiO2X-(NH)2-Pd-L2, where L = P(C6H5)3 or C6H5CN and X = Sn, Al or Ti. The catalysts were stable and could be reused several times in normal atmosphere without suffering appreciable loss in catalytic activity. The activity of the catalysts was good even at low temperature, and selectivities were very high. Strong interaction indicating the existence of chemical bonding was found between the modified silica support and palladium complex. A model of the active surface compound is proposed and confirmed.

The activity of carbonyl cluster derived Co-RuSiO2 and Co-RhSiO2 catalysts in CO hydrogenation

We studied systematically the use of tetranuclear cobalt, cobalt-ruthenium, cobalt-rhodium and rhodium carbonyl clusters as catalyst precursors. The catalytic activities and the product distributions of the hydrogenation of carbon monoxide over Co4−nRunSiO2 and Co4−nRhnSiO2 catalysts (where n = 0−4) and (Co4 + Ru4)SiO2 and (Co4 + Rh4)SiO2 catalysts derived from the transition-metal carbonyl clusters were compared. Activities were highest for the catalysts derived from homometallic clusters, and lowest for catalysts with 1:1 ratio of CoRu or CoRh. Interestingly enough, the highly active homometallic cobalt catalyst was the most resistant to deactivation. On Co4−nRhnSiO2 catalysts the deactivation was stronger on bimetallic sites and on the Co4−nRunSiO2 catalysts the deactivation was closely related to the presence of ruthenium. The selectivities for oxygenated compounds were clearly promoted by the bimetallic sites of Co-Rh catalysts. This result is very plausible since the probability to find dual active sites responsible for the formation of oxygenates is greater in bimetallic than in homometallic catalysts.

Feasibility of Autothermally Reformed Natural Gas on Anode Supported Solid Oxide Fuel Cells

Three different planar anode supported solid oxide fuel cells (SOFC) were tested with hydrogen, with autothermally prereformed natural gas from which sulfur was removed, and with autothermally prereformed natural gas that contained sulfur. The cells were obtained from Forschungszentrum Julich (FZJ), Energy research Centre of the Netherlands (ECN), and HTceramix SA (HTc). All cells were so called Real-SOFC first generation cells. Cell polarizations were first measured with hydrogen, followed by a 200 h test (25 A, 800°C) with a selected fuel, and finally cell polarizations were measured with hydrogen. When hydrogen was used as the fuel in the 200 h test, the performance for all cells was comparable and no degradation was observed. All cells underwent an initial deactivation process when reformate fuels were used but their cell voltage stabilized during the first 50 h. All cells also showed deactivation after the reformate tests when the area specific resistance values were compared to the values obtained from the hydrogen tests. The deactivation was comparable between the sulfur-free and sulfur-rich reformate tests. Sulfur-rich reformate, however, caused oscillation in cell voltages as the sulfur level in natural gas was not constant.

CO hydrogenation activity of carbonyl cluster derived Co-RuSiO2 catalysts prepared by reflux method

Abstract The applicability of a reflux method for the preparation of cluster-derived CoRu catalysts supported on silica was studied. The properties of the resulting catalysts were compared with those of the corresponding catalysts prepared by impregnation. The presence of ruthenium either as a component of a bimetallic cluster or in a physical mixture of the two metals was essential for the adsorption of cobalt on silica. The activity and selectivity of these catalysts in CO hydrogenation were different from those obtained with catalysts prepared by impregnation.

Dynamic Model of 5kW SOFC CHP Test Station

A dynamical model for a 5 kW class solid oxide fuel cell (SOFC) combined heat and power (CHP) test station has been composed using the APROS® environment. The model is based on a real test station being constructed and operated at VTT Technical Research Centre of Finland and it comprises the following main components of the real test system: the autothermal reforming unit, SOFC stack situated inside a furnace, catalytic afterburner, and three heat exchangers. The constructed model has been verified against experimental results obtained from the autothermal reforming unit, catalytic afterburner, and the two cathode side heat exchangers. The model has been used for the phenomenological studies of the system during current transient simulations using a simplified and fast zero-dimensional model including internal reforming reactions for the SOFC stack. The test station model was capable of operating at a speed of 18 times the real time using a standard personal computer.

The effect of decomposition atmosphere on the activity and selectivity of the carbonyl cluster derived Co/SiO2 and Rh/SiO2 catalysts

Abstract The effect of pretreatment atmosphere, hydrogen or carbon monoxide, on the activity and selectivity of the Rh 4 (CO) 12 /SiO 2 and Co 4 (CO) 12 /SiO 2 catalysts in CO hydrogenation was determined. The catalysts pretreated under hydrogen exhibited a higher degree of decomposition of the original cluster, higher hydrogen uptake and lower carbon content than those decomposed under CO. Therefore, some of the active sites of the catalysts were encapsulated by carbon, and in the case of Co 4 (CO) 12 poorly reducible cobalt silicates were probably also formed. The activity of the hydrogen-treated Rh 4 (CO) 12 /SiO 2 was fairly similar to that of the CO-treated catalyst, but significantly fewer oxygenates were formed. Thus, the carbon monoxide treatment appeared to facilitate the formation of oxygenates. Probably the original structure of rhodium carbonyl was better retained, and thereby some of the rhodium particles remained more dispersed under CO than under hydrogen. In the case of Co 4 (CO) 12 /SiO 2 catalysts, however, no benefit was observed in conjunction with CO pretreatment either in activity or selectivity. Most likely the CO treatment resulted in the formation of unreactive carbonaceous species which permanently blocked most of the active sites.

Real-SOFC - A Joint European Effort to Improve SOFC Durability

The Integrated Project Real-SOFC joined 26 partners from throughout Europe active in SOFC technology. The project was funded by the European Commission within the 6th Framework Programme and aimed at improving the durability of planar SOFC stacks to degradation rates of well below 1% per 1000 hours of operation. This is an essential requirement in gaining access to the market for stationary applications. The underlying idea was to improve materials and materials processing on the basis of extensive test results identifying degradation mechanisms, and then to supply industrial components of enhanced quality for repeated testing analysis. This ‘feedback loop’ resulted in ‘2 nd ’ and ‘3 rd ’ Generations of SOFC components. This paper summarises the project approach, shows examples of the major results and of longterm durability testing.

Solid Oxide Fuel Cell System Development in VTT

The Finnish solid oxide fuel cell (SOFC) project (FINSOFC) was initiated in 2002 as a five-year project. It forms the core of the publicly funded SOFC research in Finland. The purpose of the project is to support the industry in its development of SOFC systems and components and other possible SOFC-based business to be created in the future. The project is coordinated by the VTT Technical Research Centre of Finland in cooperation with universities and industrial enterprises. The project is executed in close cooperation with several European partners both bilaterally and within Real-SOFC. The focus is to construct and run a natural gas-fueled 5 kW e SOFC power plant demonstration connected to heat and electricity grids. The power plant demonstration contains a stack and all BOP components from fuel processing to power conditioning and grid connections. The aim is also to thoroughly understand the behavior of the system. The subprojects needed to do this are (i) fuel processing, (ii) testing of fuel cells and stacks, (iii) construction of a 5 kW e power station demonstration, and (iv) system modeling.

Effect of Ethene Impurity on Performance of Solid Oxide Fuel Cell

A pre-reforming unit is needed if liquid hydrocarbon fuels, such as gasoline or diesel, are used in solid oxide fuel cell (SOFC) systems. Although pre-reforming removes most of the higher hydrocarbons, there may still be some fractions left in the reformate flow. Ethene was chosen to be the subject of this work because it has been analyzed to be the most significant impurity in diesel reformate. In this work, an anode supported unit cell was used to examine the behavior and performance of a SOFC when ethene was added to hydrogen feed. The ethene concentration in the feed was increased stepwise from 0 ppm to 1000 ppm and the current was kept constant for 100 hours at each concentration level. Changes in the cell performance were monitored by impedance spectroscopy and polarization measurements. It was detected that ethene does not accelerate cell degradation.