The present invention provides methods and designs of enclosed-channel reactor system for manufacturing catalysts or supports. Both of the configuration designs force the gaseous precursors and purge gas flow through the channel surface of reactor. The precursors will transform to thin film or particle catalysts or supports under adequate reaction temperature, working pressure and gas concentration. The reactor body is either sealed or enclosed for isolation from atmosphere. Another method using super ALD cycles is also proposed to grow alloy catalysts or supports with controllable concentration. The catalysts prepared by the method and system in the present invention are noble metals, such as platinum, palladium, rhodium, ruthenium, iridium and osmium, or transition metals such as iron, silver, cobalt, nickel and tin, while supports are silicon oxide, aluminum oxide, zirconium oxide, cerium oxide or magnesium oxide, or refractory metals, which can be chromium, molybdenum, tungsten or tantalum.