Труды КНЦ вып.5 (ХИМИЯ И МАТЕРИАЛОВЕДЕНИЕ вып. 5/2015(31))

CO 2 + 4H 2 = CH 4 + 2H2O AH° = -114 kJ mol -1 (10) CO + 3H 2 = CH 4 + H2O AH° = -206 kJ mol -1 (11) 2CO + 2H 2 = CH 4 + CO 2 AH° = -247 kJ mol -1 (12) It was shown that the back WGSR is a first-order reaction, the activation energy in the Arrhenius equation Eg ' к = Ae rt is Ea = 42 kJ-mol-1: the reaction constant is к = 4.5Ы 0 " 11 s -1 (at 523 K), and the preexponential factor is 7.62T0-7 s-1. The coatings of the nickel-promoter molybdenum carbides are stable at least for 30 h. After measuring the catalytic activity, the phase composition of these coatings is unchanged. We also found no changes in the morphology of the nickel-promoter molybdenum carbides after their catalytic activity measurements. Fig.3. Micrograph o fa molybdenum-nickel alloyproduced by currentless transfer in the NaCl-KCl-NiCl2-N i melt at 1123 K for 1 hfollowed by carbonization in the NaCl-KCl-Li 2 CO 3 melt at ic = 5 mAcm ,'2 and T = 1123 K fo r 5 h (seriesA) The conversion of carbon dioxide on the synthesized catalysts is an order of magnitude higher than the conversion of CO 2 on molybdenum carbide [7]. Since methane formation is an undesirable process in WGSR, it is necessary to check the probability of methane formation in the forward water-gas shift reaction. We assume that the synthesized coatings can also be active catalysts for the forward reaction. Since metallic nickel is a catalyst for the formation of carbon due to the decomposition of methane and the disproportionation of CO, these processes can result in catalyst deactivation and the clogging of the proton-exchange membrane of a fuel element by elementary carbon, CH 4 = C(s) + 2 H 2 . (13) 2CO = C(s) +CO 2 . (14) In our case, however, we did not detect carbon formation during the back WGSR. Fig.4. Molybdenum-cobalt alloy produced by currentless transfer in the NaCl-KCl-CoCl 2 melt in contact with Co, T = 1123 K, T = 1 h, followed by carbonization in the NaC l-KC l- Li 2 CO 3 melt, ic = 5 mA cm-2, T = 1023 K, т= 3 h (a); molybdenum-cobalt alloy produced by electrolysis in the same melt, ic = 5 mA cm '2, T = 1123 K, т= 1 h, followed by carbonization ic = 5 mAcm,'2, T = 1123 K, т= 5 h (b) Apparently, the use of double molybdenum and cobalt carbides and nickel-promoter molybdenum carbides in the forward and back water-gas shift reaction makes it possible to avoid methane formation. Therefore, we will study the catalytic activities of double Mo and Co carbides and nickel-promoter molybdenum carbides. The preliminary results of synthesizing these carbides demonstrate that their surface is much more developed as compared to the nickel-containing compositions (Fig.4). The products of carbonization of the molybdenum and cobalt alloys are carbides Co 6 Mo 6 C2, Co 6 Mo 6 C, Co 3 Mo 3 C, and cobalt-promoter Mo 2 C depending on the synthesis conditions. Thus we proposed a new two-stage method for synthesizing double molybdenum and nickel carbides and nickel- promoter molybdenum carbide. It consists in electrochemical synthesis of molybdenum and nickel alloys in chloride melt followed by carbonization in chloride-carbonate melt. 223