(289c) Propane Dehydrogenation over Metal-Exchanged Small-Pore Zeolites | AIChE

(289c) Propane Dehydrogenation over Metal-Exchanged Small-Pore Zeolites


Lobo, R., University of Delaware
Small-pore zeolites ion-exchanged with metal cations such as In-CHA have been recognized as selective catalyst for non-oxidative alkane dehydrogenation, the impact of the zeolite structure on the indium speciation, however, has yet been investigated. In this work, indium on silica, alumina and zeolite CHA have been used to investigate the effect of support on the indium speciation and corresponding influence on propane dehydrogenation performance. On In-CHA, In2O3 initially located on the external surface of the H-CHA zeolite was found to displace Brønsted acid sites (BAS) in the presence of H2 at high temperature. The formation of In+ in CHA was evidenced by the stoichiometric ratio (1.5) of formed H2O to consumed H2 during H2 reduction pulses. The reduced indium species is different depending on the support—In/SiO2, In/Al2O3 and In2O3—in which a portion of the In2O3 was reduced to form In(0) species (as determined by X-ray diffraction patterns and H2 temperature-programmed reduction profiles, pulse reactor measurements and in-situ transmission FTIR spectroscopy). It is clear that the presence of BAS prevents the deep reduction of In2O3 to In(0) in CHA. We will show that the In+ in CHA can be oxidized to form indium oxide in the micropores, and reduced again to form stable In+, showing promising redox properties. At comparable conversion, In-CHA shows better stability and C3H6 selectivity (~85%) than In2O3, In/SiO2 and In/Al2O3. The ratio of C3H8 dehydrogenation rate to C3H8 cracking rate is the highest on the In-CHA, a result consistent with the low C3H8 dehydrogenation activation energy and high C3H8 cracking activation energy. These results all point to the conclusion that the dehydrogenation properties of In+ species in CHA are superior than In(0) in other supports. This investigation highlights that small-pore-zeolite-stabilized metal cations could find practical application as a highly stable and selective catalyst on alkane dehydrogenation reactions.