Fundamental insights into the oxidative dehydrogenation of ethane to ethylene over catalytic materials discovered by an evolutionary approach

An evolutionary optimisation procedure combined with high-throughput synthesis and testing has been applied for discovering new catalytic materials for the oxidative dehydrogenation of ethane to ethylene (ODHE). After 10 generations comprising a total of 600 vanadium-free catalytic compositions supported on alpha-Al2O3, Cr/Co/Sn/W and Cr/Mo mixed oxides have been identified as new well performing catalytic materials for the ODHE reaction; ethylene yields of up to 20% and selectivities of 55-65% (500degreesC; C2H6:O-2:Ar = 20:10:70) were achieved. The surface and bulk characteristics of the new catalytic materials derived from near-surface composition, binding energies of the elements (XPS), and phase analysis (XRD) as well as from their surface area (BET) lead to the assumption that for both systems (Cr/Mo or Co/Cr/Sn/W oxide) the active phase is located in the X-ray amorphous part of the material. Based on transient and isotopic experiments it was concluded that the ODHE reaction follows the Mars-Van Krevelen mechanism. The different selectivities towards CO2 and CO between the two systems have been attributed to parallel and consecutive reaction schemes of the product formation, derived from transient experiments. From the fundamental insights obtained improvements of the catalytic performance in the ODHE reaction are suggested. (C) 2003 Elsevier B.V. All rights reserved.