For preparing catalysts, there have been various methods of reducing catalyst precursors containing metal oxides proposed. For example, a copper-based catalyst is used in production of an alcohol by hydrogenation of a carboxylic acid or a carboxylic acid ester. When a fixed-bed reaction system is employed, the copper-based catalyst is entirely subjected to gas phase reduction for activation. In industry, such gas phase reduction of a catalyst is generally carefully conducted at a predetermined temperature under an inert gas flow that contains several to several tens percent of hydrogen in order to avoid local overheat due to rapid reduction of the catalyst.
In some cases, reduction of a metal oxide with hydrogen generates a large amount of heat. For example, one mole of copper oxide generates 20 kcal of reduction heat. In addition, reduced copper is known to have very low thermal stability. Thus, it is important to gradually conduct reduction with controlling heat generation to produce a copper catalyst without impairing its performance. This is particularly important for a molded catalyst, because it has a difficulty of heat release.
Therefore, it is naturally expected for a catalyst subjected to reductive activation with high concentrate hydrogen for a short time in a gas phase to have significantly decreased catalytic performance due to rapid generation of heat, and more for a catalyst subjected to reductive activation for a short time in such a large scale as in industry to fall into very serious situations due to rapid elevation of temperature. As thus, a general method for practical gas phase reductive activation of a catalyst containing copper oxide is generally conducted with low concentrate hydrogen for a long time. For instance, JP-A 61-161146 describes that such reductive activation takes a time from 4 to 14 days.
As described above, fixed-bed reaction systems generally employ gas phase reduction, but some systems employ liquid phase reduction to activate a catalyst precursor containing copper oxide. For example, JP-B 2990568 discloses liquid phase reduction of a molded precursor of a copper-containing hydrogenation catalyst, that reduction is conducted at a temperature ranging from 50 to 140° C.
JP-B 3195357 discloses activation of a copper-containing hydrogenation catalyst by supplying a mixture of hydrogen with an inert gas under an inert solvent flow.