An effect of Pt addition to improve the catalytic performance of Pd-modified Mn-hexaaluminate in the high-temperature oxidation of methane, especially in SO₂ and water presence, has been studied. X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry and differential thermal analysis were used for the characterization of fresh and spent catalysts. Temperature-programmed reduction by hydrogen was employed to study the redox properties of the catalysts. Four high-temperature tests (at 670°C) of the methane oxidation were applied to reveal the water and sulfur resistance of the catalysts: 1) dry methane-air feed; 2) wet methane-air feed containing 3wt% of water vapor; 3) methane-air feed containing 1000ppm of SO₂; and 4) wet methane-air feed with 1000ppm of SO₂. The Pt-doped Pd-Mn-hexaaluminate catalyst with the atomic ratio of Pt/Pd<0.3 has been shown to possess the highest catalytic activity in the oxidation of methane, high water and sulfur tolerance, and reducibility by hydrogen as compared to the monometallic Pd-Mn-hexaaluminate catalyst and the bimetallic catalysts with Pt/Pd>0.5. From the formal kinetic data of the oxidation of methane on the fresh and deactivated catalysts, we assumed that deactivation of the catalysts is due to a decrease in the amount of catalytically active sites in the bimetallic 0.33Pt-0.67Pd(0.27)/MnLaAl₁₁O₁₉ catalyst and a change in the state of active component in the other catalysts. Their oxidation ability and redox behavior were shown to be associated with the highly dispersed PdO particles, a PdO layer (3–5nm) covering the metal palladium particles as well as the Mn³⁺-enriched MnLaAl₁₁O₁₉. The improved water and sulfur resistance is found to correlate with the presence of particles of PtPd alloy, with its fraction not exceeding 50%.

中文翻译：

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Pt的添加对甲烷高温氧化Pd-Mn-六铝酸盐催化剂的二氧化硫和水蒸气耐受性的影响

研究了添加Pt改善Pd改性的Mn-六铝酸锰在甲烷的高温氧化中，特别是在SO ₂和水存在下的催化性能的作用。X射线衍射，高分辨率透射电子显微镜，X射线光电子能谱，热重分析和差热分析被用于表征新鲜和用过的催化剂。氢气的程序升温还原被用来研究催化剂的氧化还原性能。进行了四个甲烷氧化的高温测试（在670°C下），以揭示催化剂的耐水和硫性能：1）干燥的甲烷-空气进料；2）含3wt％水蒸气的湿甲烷空气进料；3）含1000ppm SO _2的甲烷-空气进料; 4）湿的甲烷空气进料，其中含有1000ppm的SO ₂。与单金属相比，具有Pt / Pd ＜0.3的原子比的Pt掺杂的Pd-Mn-六铝酸盐催化剂显示出在甲烷的氧化中具有最高的催化活性，高的水和硫耐受性以及氢的还原性。 Pd-Mn-六铝酸盐催化剂和Pt / Pd＞ 0.5的双金属催化剂。根据新鲜和失活催化剂上甲烷氧化的形式动力学数据，我们假设催化剂失活是由于双金属0.33Pt-0.67Pd（0.27）/ MnLaAl ₁₁中催化活性位点的数量减少Ø ₁₉催化剂和其他催化剂中活性成分状态的变化。已证明它们的氧化能力和氧化还原行为与高度分散的PdO颗粒，覆盖金属钯颗粒的PdO层（3-5nm）以及富含Mn ^3+的MnLaAl ₁₁ O _19有关。发现改进的耐水和硫性与PtPd合金颗粒的存在相关，其比例不超过50％。