Discovery from combinatorial heterogeneous catalysis - A new class of catalyst for ethane oxidative dehydrogenation at low temperatures

Combinatorial methodologies are emerging as powerful tools in heterogeneous catalysis. Previously, we have established a strong correlation between catalysts prepared as thin films for high-throughput primary screening to those prepared in bulk for secondary screening in a multi-channel fixed bed (MCFB) microreactor for the ethane oxidative dehydrogenation process [Proc. Natl. Acad. Sci. U.S.A. 96 (1999) 11077]. Numerous catalysts with improved performance over literature compositions were also reported. With this high-throughput technology, tens of thousands of new compositions have been synthesized and tested. In this paper, we describe in detail the discovery of a new class of catalysts with extraordinary performance improvements. These catalysts contain Ni, Nb, and Ta or Co mixed oxides. The respective ternary systems were first screened in a thin film form (similar to200 mug catalyst loading). Then they were scaled up to 50 mg level and screened in an MCFB microreactor. The optimal compositions were Ni0.62Ta0.10Nb0.28Ox and Ni0.62Ta0.20Nb0.18Ox. They convert 20.5% of ethane with 86.2% selectivity to ethylene and 20.0% of ethane with 86.1% selectivity to ethylene at 300 degreesC, respectively, as compared to 3.3% conversion of ethane with 82.9% selectivity to ethylene for the state-of-the-art catalyst Mo0.72V0.26Nb0.02Ox under identical testing conditions. One of these compositions, Ni0.62Ta0.10Nb0.28Ox, was further scaled up to 5 g and tested in a conventional bench scale reactor. The performance improvement is consistent with measurements made on the MCFB microreactor. (C) 2003 Elsevier Science B.V. All rights reserved.