A system for the selective removal of CO2, H2S, and H2 from a gaseous fluid mixture comprising CO2, H2S, and H2, which system includes a first membrane section having a nonporous metal oxide membrane, a second membrane section having a CO2-selective membrane, and a third membrane section having an H2-selective membrane. Each membrane section has a feed side and a permeate side and the membrane sections are arranged in series whereby the gaseous fluid mixture contacts the feed side, in sequence, of the first membrane section, the second membrane section and the third membrane section, resulting first in the separation or removal of H2S, second in the separation or removal of CO2, and third in the separation or removal of H2. The process can be used to process synthesis gas generated from the gasification or reforming of carbonaceous materials for hydrogen production and carbon dioxide capture.