A novel methanol synthesis process, the liquid-phase methanol (LPMEOH) process, has been developed and scaled up to a nominal 380 kg/h (10 ton/day) pilot plant. The process is based on a gas-sparged slurry reactor instead of a conventional, fixed-bed reactor. The use of slurry reactors, which are essentially gradientless, greatly facilitated the interpretation and quantification of catalyst deactivation phenomena. With a poison-free, CO-rich feedstream, the rate of deactivation of the Cu/ZnO catalyst increased rapidly with temperature. At constant temperature, in the absence of poisons, the decline with time in the rate constant for methanol synthesis correlated with the loss of BET surface area. Iron carbonyl, nickel carbonyl, and carbonyl sulfide are severe and highly specific poisons for methanol-synthesis catalyst. There was a linear relationship between the catalyst activity loss and the concentration of metal or sulfur on the catalyst.