Making use of synergy between urea and citric acid, a core–shell [email protected]₂ catalyst with spherical morphology was facilely synthesized by a hydrothermal method. The formation mechanism of the core–shell structure in the presence of citric acid and hydrogen peroxide was studied. Results showed that the [email protected]₂ catalyst exhibited high catalytic activity in methane oxidation. Pd nanoparticles were well stabilized by CeO₂ shell encapsulation, resulting in high stability of the catalyst. A high CH₄ conversion of 99% was retained after 50 h on-stream reaction at 500 °C. Additionally, many tiny pores on the CeO₂ shell surface were beneficial for the full contact between reactants and active components. Pd nanoparticles were highly dispersed inside the shell, improving the utilization efficiency of active components. The results also demonstrated that the Pd species in the catalyst existed in the form of oxidation state, mainly in PdO (ca. 66.6%), which played an essential part in methane combustion.

中文翻译：

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具有尿素和柠檬酸协同作用的甲烷稳定高效[电子邮件保护] ₂催化剂的合成

利用尿素和柠檬酸之间的协同作用，通过水热法轻松合成了具有球形形态的核-壳[电子邮件保护] ₂催化剂。研究了柠檬酸和过氧化氢存在下核-壳结构的形成机理。结果表明，[email protected] ₂催化剂在甲烷氧化中表现出较高的催化活性。通过CeO ₂壳包封，Pd纳米颗粒具有良好的稳定性，从而使催化剂具有很高的稳定性。在500°C下进行50 h的在线反应后，保留了99％的高CH ₄转化率。另外，CeO ₂上有许多细孔壳表面有利于反应物和活性成分之间的充分接触。Pd纳米粒子高度分散在壳内，提高了活性成分的利用效率。结果还表明，催化剂中的Pd物种以氧化态形式存在，主要存在于PdO中（约占66.6％），这在甲烷燃烧中起着至关重要的作用。