Simultaneous synthesis and hydrolysis of Zn nanoparticles was studied as the second step in a ZnO/Zn redox solar water splitting process. Nanoparticles were synthesized and hydrolyzed in a condensation nucleation process using a mixture of argon and steam to quench zinc evaporated in a hot wall tubular reactor. Hydrogen production was attributed to hydrolysis of Zn nanoparticles in the carrier gas stream and deposited on the reactor walls. Zinc oxide content of the deposited material decreased with distance downstream of the quench flow. This reduction was attributed to lowered reaction rates with decreasing temperature. This is an abstract of a paper presented at the 2007 AIChE Annual Meeting (Salt Lake City, UT 11/4-9/2007).