With a modified Pechini synthesis, mixed Ru_xIr_1−xO₂ is grown on rutile-TiO₂ with full control of the composition x, where the preformed TiO₂ particles serve as nucleation sites for the active component. Catalytic and kinetic data of the methane combustion over Ru_xIr_1−xO₂@TiO₂ and unsupported Ru_xIr_1−xO₂ catalysts reveal that the least active catalyst is RuO₂@TiO₂ (onset temperature: 270 °C), while the most active catalyst is Ru_0.25Ir_0.75O₂ with an onset temperature below 220 °C. Surprisingly, even Ru_0.75Ir_0.25O₂@TiO₂ is remarkably active in methane combustion (onset temperature: 230 °C), indicating that little iridium in the mixed Ru_xIr_1−xO₂ oxide component already improves the activity of the methane combustion considerably. We conclude that iridium in the mixed Ru_xIr_1−xO₂ oxide enables efficient methane activation, while ruthenium promotes the subsequent oxidation steps of the methyl group to produce CO₂. Kinetic data provide a reaction order in O₂ of zero, while that of methane is close to one, indicating that the methane activation is rate limiting. The apparent activation energy varies among Ru_xIr_1−xO₂ from 110 (x=0) to 80 kJ ⋅ mol⁻¹ (x=1). This variation in the apparent activation energy may be explained by the variation in adsorption energy of oxygen. Under the given reaction conditions the catalyst's surface is saturated with adsorbed oxygen and only if oxygen desorbs, methane can be activated and the methyl group can be accommodated at the liberated surface metal sites.

中文翻译：

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金红石型 TiO2 负载的混合 RuxIr1−xO2：催化甲烷燃烧，模型研究

通过改进的 Pechini 合成，混合的 Ru _x Ir _{1- x} O ₂在金红石-TiO ₂上生长，完全控制成分x，其中预先形成的 TiO ₂颗粒用作活性成分的成核位点。Ru _x Ir _{1− x} O ₂ @TiO ₂和无载体的Ru _x Ir _{1− x} O ₂催化剂上甲烷燃烧的催化和动力学数据表明，活性最低的催化剂是RuO ₂ @TiO ₂（起始温度：270 °C），而最活跃的催化剂是 Ru _0.25 Ir _0.75 O ₂，起始温度低于 220 °C。令人惊讶的是，即使 Ru _0.75 Ir _0.25 O ₂ @TiO ₂在甲烷燃烧中也非常活跃（起始温度：230 °C），表明混合的 Ru _x Ir _{1− x} O ₂氧化物组分中的少量铱已经提高了甲烷燃烧的活性。甲烷燃烧相当大。我们得出结论，混合 Ru _x Ir _{1− x} O _{2 中的}铱氧化物能够有效地激活甲烷，而钌促进甲基的后续氧化步骤以产生 CO ₂。动力学数据提供在 O ₂中的反应级数为零，而甲烷的反应级数接近于 1，表明甲烷活化是限速的。Ru _x Ir _{1− x} O ₂的表观活化能从 110 ( x =0) 到 80 kJ ⋅ mol ^-1 ( x=1）。表观活化能的这种变化可以用氧吸附能的变化来解释。在给定的反应条件下，催化剂的表面被吸附的氧饱和，只有当氧解吸时，甲烷才能被活化，甲基可以容纳在释放的表面金属位点上。