MCM41 nanoparticles with or without mercaptopropyl functional groups were added to a synthesis gas fermentation reactor to investigate their influence on syngas fermentation. Carbon monoxide was fermented using Rhodospirillum rubrum (R. rubrum), resulting in an enhanced H-2 concentration in the product gas as a result of a biologically mediated water-gas shift (WGS) reaction. The results indicated that the H2 yield was enhanced by similar to 200% when 0.6 wt% of the MCM41 nanoparticles functionalized with 5% molar ratio of mercaptopropyl group were added to the reactor. These results complement previous studies and suggest that the increased H-2 yield is due to enhanced CO-water mass transfer through the addition of the functionalized MCM41 nanoparticles. (c) 2010 Elsevier Ltd. All rights reserved.