Gas phase hydroformylation of ethylene using organometalic Rh-complexes as heterogeneous catalysts
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Catalysis Letters Vol. 101, Nos. 1–2, May 2005 ( 2005) DOI: 10.1007/s10562-004-3747-8
Gas phase hydroformylation of ethylene using organometalic Rh-complexes as heterogeneous catalysts V.I. Zapirtan, B.L. Mojet*, J.G. van Ommen, J. Spitzer, and L. Lefferts Catalytic Processes and Materials, Faculty of Science and Technology, Institute of Mechanics Processes and Control Twente (IMPACT), University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
Received 15 October 2004; accepted 3 December 2004
The heterogeneously catalysed gas phase hydroformylation of ethylene to propionaldehyde was studied over solid RhCl(PPh3)3 and RhCl(CO)(PPh3)2. At 3 bar and 185 C, an active phase formed from RhCl(PPh3)3 which was different from RhCl(CO)(PPh3)2 under the reaction conditions studied. The selectivity of RhCl(PPh3)3 to propanal was much better than that of supported Rhmetal. Thus, solid metal-complexes operated in gas phase reactions clearly hold promise as a new class of heterogeneous catalysts. KEY WORDS: ethylene hydroformylation; rhodium complex; gas phase heterogeneous catalysis; Wilkinson’s catalyst.
1. Introduction Organometallic compounds and other metal-complexes are known to be efficient homogeneous catalysts in numerous liquid phase reactions [1–3]. The main advantage of homogeneous catalysts compared to heterogeneous ones is the fact that catalytic properties can easier be tuned since the structure of the active species is better defined. However, in many applications, the separation of homogeneous catalysts from reactants and products is the most important drawback. Significant investments are often necessary to separate and re-use the catalyst and, moreover, decomposition of the catalyst and/or the ligands is frequently a key problem, especially when high temperatures are encountered in distillation sections. As a result, extensive research has been carried out to combine the advantages of homogeneous and heterogeneous catalysts by immobilizing homogeneous catalysts on solid supports. A recent review by Valkenberg and Ho¨lderich [4] gives an excellent description of the state of the art. Unfortunately, in many cases these systems are not sufficiently stable; leaching of the metalcomplexes as a result of insufficient bonding between ligands and support are general problems that have not been solved in most cases [5]. This paper describes an alternative approach to solve these problems, namely to apply organometallic complexes directly as a heterogeneous catalyst: operate the solid metal-complex in a gas-phase reaction, i.e. all reactants and products are in the gas-phase while the catalyst is solid. As such leaching is avoided by preventing the presence of any liquid phase. Obviously, this * To whom correspondence should be addressed. E-mail: [email protected]
approach is only possible as long as condensation temperatures of reactants and products are not too high. In addition, the complex needs to be sufficient stable under the applied reaction conditions. To investigate the feasibility of this method we cho
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