Classification of Methanol synthesis catalysts

The development of methanol catalysts is the cornerstone of the methanol synthesis industry and can be divided compositionally into four categories: zinc-chromium based catalysts, copper based catalysts, non-copper based catalysts and liquid phase catalysts.

1. Zinc-chromium catalysts
The zinc-chromium (ZnO/Cr2O3) catalyst was the first catalyst developed for methanol synthesis. Zn-Cr catalysts are characterised by good heat resistance and can tolerate superheating processes at temperatures above 100°C. They are insensitive to sulphur, have high mechanical strength, long service life, are resistant to toxicity, have a wide range of uses and are easy to control; compared to copper-based catalysts, they have low activity, low selectivity and are difficult to distill (complex impurities in the product). As the mass fraction of Cr2O3 in these catalysts is as high as 10%, they have become an important source of chromium pollution and are now being phased out.

2. Copper based catalysts
Copper-based catalysts are low temperature and low pressure catalysts, mainly divided into three categories: the first category is copper-zinc-chromium catalysts, consisting of copper, zinc and chromium oxides, with a small amount of other elements added, such as copper, zinc, chromium and manganese; the second category is copper-zinc-aluminium catalysts; the third category is a catalyst based on copper and zinc, with the addition of chromium and aluminium other than the third and fourth components, the activity of these catalysts is similar to that of the copper-zinc-lead system. Copper-based catalysts have the advantages of high catalyst activity, good selectivity and low operating temperature compared to zinc-chromium-based catalysts, but they have poor high temperature resistance, are sensitive to sulphur and have a low one-way conversion rate.

3. Non-copper based catalysts
Amongst the non-copper based catalysts, the ones that are considered to have a limited pathway are those with noble metals as active components, e.g. platinum, palladium and molybdenum based catalysts. Compared to copper-based catalysts, the selectivity and catalytic activity are not significantly improved and they are more expensive.
4. Liquid phase catalysts
Liquid phase methanol synthesis is gaining importance and it is estimated that the liquid phase synthesis route is 20% more economically efficient than the gas phase synthesis route for the production of methanol from syngas.