Conversion of CO to formaldehyde catalyzed by BeO: A theoretical study

Ab initio calculations at the G2M(MP2)//MP2/6-31G** level have been perform ed to investigate the potential energy surface for various reaction mechani sms in the BeO/CO/H-2(-) system. The results show that the conversion of ca rbon monoxide to formaldehyde can be catalyzed by beryllium oxide in the ga s phase. Two different reaction mechanisms have been suggested. In the firs t one, BeO + CO + H-2 --> OBeOC + H-2 --> OBeOCH2 --> BeO + H2CO, BeO first reacts with CO to form the OBeOC complex (bound by 20.2 kcal/mol), which i nteracts with H-2 to give the complex between BeO and H2CO via a barrier of 53.1 kcal/mol relative to the initial reactants, and OBeOCH2 decomposes to BeO + formaldehyde without an exit barrier but with endothermicity of 44.9 kcal/mol. In the second mechanism, BeO + H-2 + CO --> HBeOH + CO --> t-HCO BeOH --> OBeOCH2 --> BeO + H2CO, the initial step is the reaction of BeO wi th molecular hydrogen exothermic by 88.3 kcal/mol. Then, CO inserts into th e Be-H bond of HBeOH to form the HCOBeOH intermediate, 80.2 kcal/mol below the reactants, which undergoes a 1,3-hydrogen shift from carbon to oxygen y ielding the OBeOCH2 complex and the latter decomposes to the final, product s., On this pathway, the highest barrier is found for the t-HCOBeOH --> OBe OCH2 hydrogen shift step with a transition state lying only 5.4 kcal/mol ab ove BeO + H-2 + CO, thus making the gas-phase reaction possible even at low temperatures. The reverse reaction of the H2CO decomposition to H-2 + CO c an be also catalyzed by BeO in the gas phase, since the barrier decreases f rom similar to 80 kcal/mol for the unimolecular dissociation to only 2.0 kc al/mol for the reaction in the presence of BeO.