Modification of carbon materials for catalyst applications

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Emma Sairanen Name of the doctoral dissertation Modification of carbon materials for catalyst applications Publisher School of Chemical Technology Unit Department of Biotechnology and Chemical Technology Series Aalto University publication series DOCTORAL DISSERTATIONS 21/2015 Field of research Chemical Technology Manuscript submitted 8 September 2014 Date of the defence 10 April 2015 Permission to publish granted (date) 9 December 2014 Language English Monograph Article dissertation (summary + original articles) Abstract Sustainable methods to produce chemicals and energy are widely studied and the use of catalysts is notable as a means to make processes more efficient and selective. Carbon materials have many properties that can be utilized in catalyst applications. In this thesis, carbon was studied as a catalyst material and different carbon catalyst preparation methods were applied. The prepared catalysts were tested in xylose dehydration and alcohol electrochemical oxidation reactions. Cinnamaldehyde hydrogenation was used as a model reaction for characterization of part of the prepared catalysts.Sustainable methods to produce chemicals and energy are widely studied and the use of catalysts is notable as a means to make processes more efficient and selective. Carbon materials have many properties that can be utilized in catalyst applications. In this thesis, carbon was studied as a catalyst material and different carbon catalyst preparation methods were applied. The prepared catalysts were tested in xylose dehydration and alcohol electrochemical oxidation reactions. Cinnamaldehyde hydrogenation was used as a model reaction for characterization of part of the prepared catalysts. Carbon materials can act as catalysts without any metals if the surface contains suitable heteroatoms. Functionalization of carbon surfaces by oxidation treatment was used to create these different type oxygenand sulphur-containing acidic and basic sites on the surface. The carbon materials were used as catalyst supports and tested as catalysts for xylose dehydration using water as a solvent. Carbon was found to be a selective and stable catalyst towards furfural formation. Three different methods for preparing carbon supported Pd, Pt, and PtCo metal catalysts were tested: the traditionally used dry and wet impregnation methods with liquid precursors and the less commonly used gas-phase deposition method based on atomic layer deposition (ALD). The ALD based preparation method was found to lead to catalysts with the highest metal dispersion and smallest metal particles with a narrow metal particle size distribution. Monoand bi-metallic catalysts were prepared by ALD and these catalysts were tested for electrochemical oxidation of alcohols. Mono-metallic ALD-prepared Pd catalysts gave higher current densities compared to similar commercial Pd fuel cell catalysts providing the possibility to lower fuel cell catalyst costs, as the same activity is obtained with lower metal loadings. With bi-metallic PtCo catalysts, the metal growth mode on the catalyst support was studied. Metal growth on the surface was found to follow mainly the island growth mode where metals attach on the surface more easily if there already are metals on the surface. The stability of the catalyst in alcohol electrochemical oxidation could be modified by adjusting the preparation parameters: with varying order of precursor cycles in ALD, the catalyst deactivation rate was lowered.