Selective hydrogen combustion in the presence of propylene and propane over Pt/A-zeolite catalysts

摘要

The behavior of selective hydrogen combustion (SHC) in the presence of propylene and propane changing with reaction temperature in a range of 100-600 degrees C has been investigated over the Pt catalysts supported on A- zeolites. The effect of Pt loading varying from 0.01 to 2 wt% on the catalytic SHC performance has been studied in the conditions with a feed gas molar composition of C3H8/C3H6/H-2/O-2 = 4/4/4/2 balanced with N-2 and gas hourly space velocity of 15,000 h(-1). The results show that for each Pt/3A catalyst having a different Pt loading there is a maximum of H-2 conversion by combustion appearing between 300 and 400 degrees C, while the selectivity to comprehensive H-2 conversion can maintain 100% when the temperature lower than 300 degrees C. Moreover, the Pt/3A catalyst with a Pt loading of 0.5 wt % performs better than the others at the temperatures higher than 300 degrees C. The maximal H-2 combustion achieved over the 0.5 wt% Pt/3A catalyst is as high as 96.6% along with a selectivity of 100% at 300 degrees C, and a 92.4% H-2 combustion with 98.5% selectivity can be obtained even if at 500 degrees C. The characterization of the catalysts reveals that the distribution of Pt atoms and the number of atoms in Pt clusters may be the key factors for giving rise to the good SHC performance. The influence of three types of A-zeolite supports on the Pt catalyzed SHC process has also been investigated. 3A zeolite is superior to 4A and 5A for supporting 0.5 wt% Pt catalyst in terms of both activity and selectivity. The lower C3H6 conversion on the 0.5 wt% Pt/3A catalyst compared to the 0.5 wt% Pt/5A may be ascribed to the insufficient sites for the C3H6 activation on the surface of Pt/3A due to the limitation of 3A channels inaccessible to C3H6 This contrarily brings about the better SHC performance on the 0.5 wt% Pt/3A catalyst. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.