Abstract

The effect of a lithium nitrate (LiNO₃) modifying additive on the genesis of the phase composition of alumina–chromium catalysts has been studied using the differential dissolution (DD) and X-ray diffraction (XRD) methods. It has been shown that LiNO₃ reacts with a pure support (Al₂O₃) to form lithium aluminate, double oxide Al₄Li₂O₇ with a spinel structure, and mixed hydroxide LiAl₂(OH)₇(H₂O)₂. The reaction of an alumina–chromium catalyst with LiNO₃ also leads to the formation of lithium aluminate and double oxide Al₄Li₂O₇; however, a mixed hydroxide is not formed. In addition, the reaction of lithium cations with the Cr(VI) catalyst active component leads to the formation of lithium chromate. A comparative analysis of the phase compositions of alumina–chromium catalysts with LiCl and LiNO₃ additives has been conducted. It has been found that, depending on the nature of the additive, the phase composition of the catalyst partially changes. In the case of the introduction of lithium chloride, solid solutions of Cr(III) and Li(I) in alumina are formed; the use of lithium nitrate leads to the formation of double oxide Al₄Li₂O₇ and lithium aluminate. The results of studying the activity of 0.5–3% Li + 9.5% Cr + Al₂O₃ catalyst samples (Li being introduced from LiCl and LiNO₃) have shown that the replacement of the LiCl modifying additive by LiNO₃ leads to a change in the catalytic properties of the alumina–chromium catalysts. The activity of the sample doped with lithium nitrate is 4–8% higher than the activity of the sample doped with lithium chloride. This finding can be attributed to the fact that, in the case of the LiNO₃ additive, the concentration of the formed active phases Li₂CrO₄ and Cr₂O₃ is higher. The selectivities of the catalysts modified with lithium salts (chloride and nitrate) differ only slightly owing to the formation of identical active phases.

中文翻译：

---

硝酸锂掺杂对氧化铝-铬催化剂相组成的影响

摘要

已经使用微分溶解（DD）和X射线衍射（XRD）方法研究了硝酸锂（LiNO ₃）改性添加剂对氧化铝-铬催化剂相组成的影响。已经表明，LiNO ₃与纯载体（Al ₂ O ₃）反应形成铝酸锂，具有尖晶石结构的双氧化物Al ₄ Li ₂ O ₇和混合氢氧化物LiAl ₂（OH）₇（H ₂ O）。₂。氧化铝铬催化剂与LiNO ₃的反应还导致铝酸锂和双氧化物Al的形成₄ Li ₂ O ₇ ; 但是，不会形成混合氢氧化物。此外，锂阳离子与Cr（VI）催化剂活性成分的反应导致形成铬酸锂。对含LiCl和LiNO ₃添加剂的氧化铝-铬催化剂的相组成进行了比较分析。已经发现，根据添加剂的性质，催化剂的相组成部分改变。在引入氯化锂的情况下，在氧化铝中形成了Cr（III）和Li（I）的固溶体。硝酸锂的使用导致形成双氧化物Al ₄ Li ₂ O ₇和铝酸锂。研究0.5–3％Li + 9.5％Cr + Al ₂ O ₃催化剂样品（从LiCl和LiNO _3中引入Li）的活性的结果表明，用LiNO ₃代替LiCl改性添加剂会导致变化氧化铝铬催化剂的催化性能。掺杂硝酸锂的样品的活性比掺杂氯化锂的样品的活性高4–8％。该发现可以归因于以下事实：在使用LiNO ₃添加剂的情况下，形成的活性相Li ₂ CrO ₄和Cr ₂ O ₃的浓度较高。更高。锂盐（氯化物和硝酸盐）改性的催化剂的选择性仅因形成相同的活性相而略有不同。