(1) supplying a feed mixture comprising the alkyne, the olefin, and molecular hydrogen into a converting zone;

(2) supplying a molecular-oxygen-containing gas stream into the converting zone; and

(3) during an oxidation interval, contacting the feed mixture and the molecular oxygen with a converting catalyst in the converting zone to produce a converted effluent, wherein the converting catalyst is contaminated before the oxidation interval by one or more of coke, a heavy hydrocarbon, a poison comprising one or more of: arsenic and/or a compound thereof, mercury and/or a compound thereof, a nitrogen-containing compound, a phosphorous-containing compound, a sulfur-containing compound, a halogen-containing compound, a transition metal and/or a compound thereof, an alkali metal and/or a a compound thereof, and an alkaline earth metal and/or a compounds thereof, to convert at least a portion of the alkyne to the olefin, and to enhance the activity and/or selectivity of the converting catalyst.