Method of regenerating ruthenium catalysts for the hydrogenation of benzene

A method for hydrogenating benzene to cyclohexane consisting of the following steps:

• a) Providing benzene and a ruthenium catalyst, wherein the ruthenium catalyst is selected from among the following groups;
• i) A catalyst comprising, as active metal, ruthenium alone or ruthenium together with at least one metal of transition group IB, VIIB or VIII of the periodic table of the elements in an amount of from 0.01 to 30% by weight, based on the total weight of the catalyst, applied to a support, wherein from 10 to 50% of the pore volume of the support is formed by macropores having a pore diameter in the range from 50 nm to 10,000 nm and from 50 to 90% of the pore volume of the support being formed by mesopores having a pore diameter in the range from 2 to 50 nm, with the sum of the pore volumes being 100%;
• and
• ii) A coated catalyst comprising, as active metal, ruthenium alone or ruthenium together with at least one further metal of transition group IB, VIIB or VIII of the Periodic Table of the Elements applied to a support comprising silicon dioxide as support material, wherein the amount of active metal is <1% by weight, based on the total weight of the catalyst, and at least 60% by weight of the active metal is present in a shell of the catalyst to a penetration depth of 200 μm, determined by means of SEM-EPMA (EDXS);
• b) Hydrogenating the benzene by contact with hydrogen in the presence of the ruthenium catalyst until the catalyst has a reduced hydrogenation activity,
• c) Regenerating the catalyst consisting of flushing with inert gas until an activity of >90% of the original activity has been attained, and
• d) Optionally, repeating steps a) to c);
• wherein step c) is carried out without removal of the catalyst, and
• wherein the pressure applied during flushing is from 0.5 to 5 bar.