The paper gives the results of experiments aimed to study start-up characteristics and the ignition limit of recombiners containing two various types of catalysts, namely ceramic rods and high porosity cell material. Both types of catalysts were produced by Redkino Catalyst Company. Experiments were carried out using a 15 m(3) BM P chamber located at the FSUE "RFNC-VNIITF named after Academ. E.I. Zababakhin " test site. The recombiner was tested in a homogeneous hydrogencontaining gas mixture under the quasi-stationary conditions with a stepwise increase in hydrogen concentration.& nbsp;Experimental results demonstrated that similar physical processes were observed for both types of catalysts. The recombiner was shown to start up when natural convection flow was activated through its case. Ignition was proved to be caused not only by a heated catalyst, but also by particles escaping from catalytic surface due to spallation and thus decreasing the ignition limit from 10% down to 5%.