The radiolysis of mixtures of carbon dioxide and hydrogen

Abstract

The self-radiolysis of COZ in excess tritium (3Hz) has been studied at pressures of 0.1 to 1.0 atm, temperatures of -80' to +lOO"C, and in the presence of added HzO, He, or Ar. The primary products of decomposition are C O and 3Hz0. Secondary products are C3H4, CzaH4, and a white polymer. The rates of disappearance of COI and formation of products and G-values were measured. The disappearance of COZ initially obeys firstorder kinetics, then slows down with time at a rate depending upon the initial pressure of 3Hz. The initial rates are proportional to pressures of COZ and 3Hz. They are independent of temperature, decreased by addition of HzO vapor, and increased by addition of He or Ar. The proposed mechanism of decomposition of COZ and formation of products involves ionization of COS followed by dissociative recombination forming C O and 0. Then the 0 reacts with a hydrogen-containing species forming OH and H20, and a back reaction forms COX from CO and OH.

The radiolysis of mixtures of carbon monoxide and hydrogen

“…rates for all isotopes. The rate of disappearance of COZ agrees, within experimental error, with the calculated rate of ionization of COZ, as it did in the absence of CO [6]. During the first 10-50 hr of CO decomposition, a minor peak grew at a massto-charge ratio of 3 1 (m/e 3 l), corresponding to C3H0, a likely fragment of C3H20.…”

“…Conversely, when water was removed from the reaction by keeping the temperature of the cold finger substantially below the freezing point of water, the rate of formation of CO2 was almost zero (runs 21 and 22). This was also observed in the COz-3H2 system [6] by the absence of a back reaction in COz decompositions at low temperatures.…”

“…The table also includes the rates of ion pair formation for COf and HZ+, which were calculated as described in ref. [6]. For the purpose of comparing this work with others, the yields have been calculated from the initial rates [6].…”

“…[6]. For the purpose of comparing this work with others, the yields have been calculated from the initial rates [6]. Yields obtained over longer time spans would be lower than the values listed.…”

“…The polymer was not initially formed during decomposition of mixtures of GO2 and 3H2 [6]. In the radiolysis of a mixture of CHI, H 2 0 , and 3H2, C 0 2 and a very low concentration of CO were formed, but no visible polymer was formed.…”