Sol-Gel and Solution Combustion Synthesized Ni/Al2O3 Catalysts for Aqueous-Phase Reforming of Ethanol

Monday, November 8, 2010: 4:18 PM
150 D/E Room (Salt Palace Convention Center)
Banasri Roy, Chemical Engineering, New Mexico Tech, Socorro, NM and Corey Leclerc, Chemical Engineering, New Mexico Institute of Mining and Technology, Socorro, NM

Aqueous phase reforming (APR) is a single step and low temperature (≤500K) energy efficient process, which can produce hydrogen as alternative energy source from water-diluted oxygenated hydrocarbons directly from fermentation, eliminating the energy intensive distillation of ethanol/water mixtures. The typical operating pressure and low temperature for APR can be helpful for the separation of H2 and CO2 from other products that are volatile at atmospheric pressure. Additionally, APR is useful for producing fuel cell grade H2 with small amount of CO in a single chemical reactor as a consequence of the water–gas shift (WGS) reaction thermodynamically favored at lower temperature reaction condition. We have investigated the catalytic effect of alumina support based nano-scale nickel catalysts for aqueous-phase reforming of ethanol. The Ni/Al2O3 catalysts were prepared by a sol-gel (SG) method and a solution combustion synthesis (SCS) route. Compared to SG and commercial catalyst the SCS sample showed • Higher EtOH conversion, H2 production, and H2 selectivity • Lower CO production and CO selectivity In order to understand these catalytic activity results we ran a series of microstructural and temperature programmed characterizations. The findings of these experiments are as follows: • Compared to the commercial and SG powders the particle size of SCS Al2O3 support is much smaller (XRD) and surface area is much higher (BET). • Compared to the commercial sample Ni-Al2O3 interaction is much stronger for SCS and SG powders (TPR) • After being used in reactor the SCS catalyst showed less carbon deposition than that of the SG and commercial powders (TPO) • Bright field TEM showed nano structure and wide dispersion of Ni metals on SCS Al2O3 sample. The particle size analyzed from TEM images match well with the sizes calculated from the corresponding XRD profile. The SCS sample clearly has higher surface area and smaller particle size which lead to higher catalytic activity. In a separate experiment the effect of surface modification of SCS alumina support powder on aqueous-phase reforming of ethanol has been explored. The surface of the Al2O3 powder was modified by a nonthermal RF plasma treatment using nitrogen gas. The catalytic activity results showed that while nature, relative ratio and selectivity of the products both in gas and liquid effluents did not change, catalytic activity of the sample increased after plasma modification. Microstructural (XRD, surface area) analysis showed that phase content and surface area of unmodified and modified catalysts are very similar, H2-chesorption shows higher metal surface area, higher metal dispersion and lower active metal particle size for the modified sample compared to the unmodified sample. The temperature programmed reduction (TPR) analysis demonstrated stronger support-metal interaction and smaller NiO particles for the modified catalyst at lower heat treatment temperature. The temperature programmed desorption (TPD) of ammonia analysis showed stronger acidity for the modified support, which can explain better dispersion of the metal particles on the modified catalyst compared to the unmodified sample.

Extended Abstract: File Not Uploaded