Alkali and alkaline-earth metal cation co-modified NaY zeolites were systematically synthesized and comprehensively investigated as catalysts for gas-phase dehydration of lactic acid (LA) to acrylic acid (AA). The long-term (time-on-stream >55 h) catalytic performance in four repeated reaction–regeneration cycles was studied. The best performing catalyst shows a consistently high AA selectivity of ∼84% at different weight hourly space velocity (WHSV) values ranging from 0.48 to 4.8 h⁻¹. Most importantly, the catalyst can still deliver a high AA selectivity of ∼82% after four long-term reaction–regeneration cycles. The investigation shows that mild etching increases the defect density of the zeolite and thus leads to poor hydrothermal stability in the long-term reaction–regeneration cycles. The strong acidic adsorbate/catalyst surface interaction (base property) and the acidity of the catalyst are responsible for the catalyst deactivation. The role of the alkali and alkaline-earth metal cations and the transformation of these cations during the reaction and regeneration process are presented.

中文翻译：

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在碱金属和碱土金属共改性的NaY沸石上将乳酸选择性转化为丙烯酸

系统地合成了碱金属和碱土金属阳离子共改性的NaY沸石，并将其作为乳酸（LA）气相脱水成丙烯酸（AA）的催化剂进行了全面研究。研究了在四个重复的反应-再生循环中的长期（运行时间> 55小时）催化性能。性能最好的催化剂在0.48至4.8 h ^-1的不同重量小时空速（WHSV）值下，显示出始终如一的高84％AA选择性。。最重要的是，经过四个长期的反应-再生循环，催化剂仍可提供约82％的高AA选择性。研究表明，温和的蚀刻会增加沸石的缺陷密度，从而在长期的反应-再生循环中导致不良的水热稳定性。强烈的酸性吸附物/催化剂表面相互作用（碱性质）和催化剂的酸度是造成催化剂失活的原因。介绍了碱金属和碱土金属阳离子在反应和再生过程中的作用以及这些阳离子的转化。