This study focuses on the conversion of bio-syngas obtained from biomass gasification to synthetic natural gas (SNG). It evaluates the kinetic sensitivity of Ni based catalysts to various poisons, in parallel with metal particle sintering occurring under SNG conditions. From a combination of state-of-the-art DRIFT/SSITKA operando techniques, a rationale of these aging processes is proposed on the basis of a direct evaluation of active reacting intermediates nature and concentration. The reversible poisoning of N and Cl containing species affects essentially surface controlling steps such as hydrogenation of CHx intermediates deriving from carbonyls decomposition, via a reversible electronic transfer from Ni to the electrophilic additives. A reverse effect would characterize the promoting effect of alkali addition. For tar-type hydrocarbons, the absence of electronic effects explain their negligible toxicity, unless surface coking and diffusion limitation. S containing molecules neutralize part of the catalytic bed without changing the reactivity of the unpoisoned metal.