Catalyst Properties and Catalytic Performance of Char from Biomass Gasification

Gasification provides a mechanism to convert solids, such as biomass, coal, or waste, into fuels that can be easily integrated into current infrastructure. This paper discusses the use of residual char from a biomass gasifier as a catalyst for tar decomposition and presents an investigation of the catalytic properties of the char. Poplar wood was gasified in a fluidized bed reactor at temperatures ranging from 550 to 920 degrees C in reaction environments of 90% steam/10% N-2 and 90% N-2/10% CO2. The properties of the char recovered from the process were analyzed, and the catalytic performance for hydrocarbon cracking reactions was tested. Brunauer-Emmett-Teller (BET) measurements showed that the surface area of the char was higher than conventional catalyst carriers. The surface area, which ranged from 429 to 687 m(2) g(-1) increased with temperature and reaction time. The catalytic activity of the char was demonstrated through testing the catalytic decomposition of methane and propane to produce H-2 and solid carbon. Higher char surface area resulted in increased performance, but pore size distribution also affected the activity of the catalyst, and evidence of diffusion limitations in microporous char was observed. Clusters of iron were present on the surface of the char. After being used for catalytic applications, carbon deposition was observed on the iron cluster and on the pores of the char, indicating that these sites may influence the reaction. When the char was heated to 800 degrees C in an inert (N-2), atmosphere mass loss was observed, which varied based on the type of char and the time. ESEM/EDX showed that when char was heated to 1000 degrees C under N-2, oxygen and metals migrated to the surface of the char, which may impact its catalytic activity. Through investigating the properties and performance of biomass gasification char, this paper demonstrates its potential to replace expensive tar decomposition catalysts with char catalysts, which are continuously produced on-site in the gasification process.