Pt particles were supported on three carbon substrates, namely multiwalled carbon nanotube, activated carbon, and Vulcan XC-72. Corresponding hydrophobic Pt catalysts for interphase H/D isotope separation were then fabricated. Catalytic performance tests demonstrated that selection of an appropriate carbon substrate is a very effective approach to improve hydrophobic catalytic activity and reduce Pt usage. The activated carbon-based hydrophobic catalyst had the lowest activity of the three carbon substrate-based hydrophobic catalyst. The multiwalled carbon nanotubes, either as a substrate for Pt particles or as an addition to the traditional Vulcan XC-72-based hydrophobic catalyst, promoted catalytic activity of the hydrophobic catalyst. The physicochemical characterizations of the carbon substrates, the carbon-supported Pt catalyst, and the hydrophobic catalytic membranes were analyzed. The characterization results explained why these hydrophobic catalysts had different catalytic activities. (C) 2010 Elsevier B.V. All rights reserved.