The interaction of hydrogen with LaNi3.5Cu1.5 - a catalyst for hydrogenation of organic compounds - was studied in a wide temperature range (308-373 K) by the Tian-Calvet differential heat-conduction calorimetry. The P-C-T-, Q-C-T-diagrams and the results of mathematical treatment of the calorimertic data are presented. The formation mechanism of active hydrogen solved in metal matrix is proposed.