关键词: 催化剂, 酯化, 加氢, 反应动力学, 低温甲醇合成, Cu/ZnO, 原位红外, 免还原

Abstract:

Conventional production of methanol is very inefficient since only 10%-15% one-pass conversion is achieved typically at 5.0-10.0 MPa and 523-573 K due to the severe thermodynamic limitations of its exothermal reaction (CO + 2H₂ = CH₃OH). A novel route of low-temperature methanol synthesis developed by Tsubaki et al from CO₂-containing syngas only by adding alcohols including methanol itself is reviewed. These alcohols act as the homogeneous co-catalysts and solvent, realizing 70%-100% one-pass conversion at only 5.0 MPa and 443 K. The key step is the reaction of the adsorbed formate species with alcohols to yield ester species at low temperatures, followed by the hydrogenation of ester by hydrogen atoms on metallic Cu. This changes the normal reaction path of conventional, high-temperature methanol synthesis from formate via methoxy to methanol. A series of new methods, such as sol-gel auto-combustion, solid-state combustion and formic acid assisted combustion methods, to prepare highly active metallic Cu/ZnO catalysts without further reduction are also reviewed. During the decomposition of metal-contained precursors in an argon atmosphere, H₂ and CO are liberated and act in situ as the reducing agents to obtain pure metals and metallic catalysts. The X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive spectroscopy, and temperature-programmed reduction analysis reveal that the as-prepared catalyst without further reduction is converted into metallic Cu⁰ and ZnO species.

Key words: catalyst, esterification, hydrogenation, reaction kinetics, low-temperature methanol synthesis, Cu/ZnO, in-situ FT-IR, reduction-free