Deacons Process — the NEET Chemistry reaction: mechanism, reagents, conditions, structures and exam traps.
Deacon's Process Deacon's process is the catalytic oxidation of hydrogen chloride gas with oxygen (air) over cupric chloride to produce chlorine and water. It historically served as an industrial route to chlorine before large-scale electrolytic processes, and remains a textbook example of heterogeneous redox catalysis. Greenish-yellow chlorine gas with a choking smell emerges with steam; the hot catalyst bed appears green (CuCl2) and can pale locally (CuCl) under reducing zones, regaining green in air. Downstream cooling condenses water; residual HCl is absorbed, and Cl2 is dried (e.g., with conc. H2SO4) and collected. Exothermic ( H 298 −114 kJ per 4 mol HCl). The reaction is equilibrium-limited and reversible; lower temperatures favor products but sufficient temperature (~720 K) is needed for acceptable kinetics and catalyst activity. Removing H2O and using excess O2 shift equilibrium toward Cl2. 1. Adsorption: HCl(g) and O2(g) adsorb on the hot CuCl2-coated porous support at ~720 K; HCl undergoes dissociative adsorption to surface H+ and Cl−. 2. Surface oxidation of chloride: Cu2+ centers (as CuCl2) oxidize chloride to chlorine while being reduced to Cu+: 2 , Cu 2+ (surf) + 2 , Cl - (ads) 2 , Cu + (surf) + Cl 2(ads) . 3. Re-oxidation of the catalyst by oxygen: Adsorbed O2 reacts with surface Cu+ and protons to regenerate Cu2+ and form water: 1 2 , O 2(ads) + 2 , H + (ads) + 2 , Cu + (surf) H 2O (ads) + 2 , Cu 2+ (surf) . 4. Desorption and product removal: Cl 2 and H 2O desorb; continuous removal of water vapour (by cooling/absorption downstream) and use of excess air drive the equilibrium forward. 5. Catalytic cycle continuity: The CuCl2/CuCl redox pair cycles between Cu2+ and Cu+ without net consumption; overall: 4 , HCl (g) + O 2(g) 2 , Cl 2(g) + 2 , H 2O (g) . Confusing Deacon’s catalyst (CuCl2) with V2O5 from the Contact process. Assuming high pressure is required—Deacon’s process typically runs near 1 atm with excess air. Forgetting the reaction is exothermic; too high T shifts equilibrium backward and lowers Cl2 yield. Mixing up Deacon’s oxidation of HCl with electrolytic chlor-alkali (brine electrolysis) or the MnO2/K2Cr2O7 lab method.