Rare earth elements: Properties and applications to methanol synthesis catalysis via hydrogenation of carbon oxides

Methanol (CH₃OH) is an important industrial chemical with a wide variety of uses. Industrial methanol synthesis catalysts are typically composed of Cu, Zn, and Al, but the use of catalysts incorporating rare earth elements has been shown to improve the catalytic performance. Due to their unique chemical and physical properties, the use of rare earth elements (scandium, yttrium, and the lanthanides) in catalysis in general has continued to increase over the past few decades, while the use of rare earth in methanol synthesis catalysts has not, despite often improving performance. The ability of several of the rare earth elements (Pr, Ce, Eu, Tb, Yb) to easily switch between oxidation states makes them beneficial for many different types of catalysts. However, for methanol synthesis the surface basicity is an important property, and the basic nature of the rare earth elements can be used to tune the basicity of catalysts. A small number of correlations between rare earth properties and catalytic performance have been observed, but often do not apply to other catalysts. Properties such as strength of basic sites, ionic radius, and electronegativity have been found to correlate with performance results such as activity or selectivity.