The hydrogen-oxygen reaction on lanthanide oxidesIX. The hydrogen-oxygen reaction on holmium oxide

The stoichiometric hydrogen-oxygen reaction has been studied over holmium oxide at an approximately constant initial hydrogen pressure in the range 160 to 250 N m −2 over the temperature range 449 to 768 K, and at different initial hydrogen pressures from 80 to 710 N m −2 at 516, 567, and 626 K. In addition, stoichiometric reactions have been conducted at 487, 550, 551, 630, 690, and 744 K after pretreatment of the catalyst with hydrogen or oxygen. Nonstoichiometric reactions have been studied at 486, 548, 630, 690, and 748 K, at initial hydrogen pressures from 20 to 360 N m −2 (740 N m −2 at 548 K), and at hydrogen-oxygen ratios from 0.20 to 5. After detailed kinetic analysis it is shown that the results fit an equation of the form: − d P T d t = k ( b H 2 P H 2 ) x b O 2 P O 2 ( 1 + b H 2 P H 2 + b O 2 P O 2 ) 1 + x where k is a proportionality constant, b H 2 and b O 2 are the adsorption coefficients for hydrogen and oxygen, respectively, P T is the total pressure of hydrogen plus oxygen, P H 2 and P O 2 are the partial pressures of hydrogen and oxygen, respectively, and x = 1 or 2. The mechanism involves the competitive adsorption of molecular hydrogen and oxygen, with the rate-determining step involving the interaction between adsorbed hydrogen molecules and adsorbed oxygen or hydrogen peroxide (double hydroxide groups).