A two catalyst system is described having separate catalyst beds for the selective conversion of acetylene to ethylene which reduces the concentration of acetylene, dienes, O2, and NOx is disclosed. An ethylene containing gas stream, such as an off-gas stream from a refinery catalytic cracking unit used in the production of fuels and gas oils, is treated by first contacting the gas stream with a silver catalyst supported on a metal oxide and subsequently contacting the gas stream with a ruthenium catalyst supported on metal oxide. The two catalysts are contained within contiguous continuous reactors or reactor compartments.