(693c) Development of Novel Carbon Nanotubes Supported Catalysts for Fischer–Tropsch and Higher Alcohol Syntheses

Abstract

Fischer-Tropsch (FT) and higher alcohol synthesis (HAS) processes are important for the conversion of synthesis gas (syngas) to liquid fuels. These fuels are free from sulfur and nitrogen compounds and are thus quite clean with high octane and cetane numbers. In this presentation, the feasibility of using new nanocatalyst formulations for FT and HAS are discussed with a focus on the conversion of syngas to green diesel and alcohols. For FT synthesis, the effectiveness of both unpromoted and promoted Fe and Co on carbon nanotubes (CNTs) is examined. The effects of pore diameter and structure of iron and iron catalysts supported on CNTs on FT reaction rates and product selectivity are presented. Two types of CNTs with different average pore sizes (12 and 63 nm), however with comparable surface area, were examined. The CNTs were prepared by chemical vapor deposition method, where as the metals were loaded with incipient impregnation method and the catalysts were characterized by ICP, BET, XRD, TPR, SEM and TEM analyses. According to TEM images of iron catalysts supported on narrow pore CNTs (np-CNT) and wide pore CNTs (wp-CNT), a majority (~80%) of the iron oxide particles were deposited inside the nanotubes’ pores. These particles on the Fe/wp-CNT (17 nm) were larger than those on Fe/np-CNT sample (11 nm). Also, the degree of reduction and metal dispersion of the Fe/np-CNT catalyst was much higher compared to the other catalyst leading to better FTS in terms of CO conversion and C₅+ selectivity of the np-CNT catalyst. In addition, novel cobalt catalyst supported on CNTs promoted with Co, Ru and K with low deactivation was created, extensively characterized and studied for FT reactions. The data show that the catalyst is quite promising with high catalyst activity and C₅+ selectivity. A series of alkali and metal (Rh and Co) promoted MoS₂ catalysts supported on CNTs were prepared and extensively tested for HAS reactions in a fixed-bed system. Our research has shown that the total alcohol space time yield (STY) using trimetallic catalyst is 0.281 g/g of cat.h at optimum reaction conditions.