In situ FTIR study on reactin pathways in Ni(CO)_4/CH_3OK catalytic system for low-temperature methanol synthesis in a liquid medium

摘要

An in situ infrared spectroscopic study was conducted to elucidate the reaction pathways for low-temeprature methankol synthesis in a catalytic system composed of Ni(CO)_4 and CH_3OK (denoted as Ni(CO)_4/CH_3Ok). The reaction was conducted in a liquid medium at 313-333 K with an initial pressure of 3.0MPa. When CH_3OK was added to Ni(CO)_4 solution at 293 K, different carbonylnickelates, [Ni_5(CO)_(12)]~(2-), [Ni_6(CO)_(12)]~(2-) and [Ni(CO)_3(COOCH_3)]~)-, were immediately formed from Ni(CO)_4. The species and the composition of the carbonylnickel compelxes varied with temeprature. The variations in concdntratins of methanol (MeOH) and methyl formate (MF) during the run, which were determined from their IR absorptions, indicated a pattern characteristic of consecutive reactions with MF as an intermediate. Thus, it was shown that methanol was produced throught he carbonylatin of MeOH to MF and the subsequent hydrogenation of MF to MeOH. Stable hydridocarbonylnickel anions, [HNi(CO)_3]~- and/or [HNi_2(CO)_6]~-, were observed together with a small amount f Ni(CO)_4 throughout the methanol synthesis. Since Ni(CO)_4 alone showed no activity for the hydrognation of MF, the hydridocarbonylnickel anions generated in the presence of Ch_3OK must be responsible for the reaction. The dual role of CH_3OK in the catalystic system was stated.