摘  要

甲醛（CH₂O）是化工行业中具有重要地位的大宗化学品，是化工工业的基础原料之一，通过选择性氧化甲醇（CH₃OH）来制备甲醛是目前生产中常用方法。这其中，催化剂是控制反应效率和最终产物质量的关键因素。铁钼法是以钼酸铁为催化剂选择性氧化甲醇制备甲醛的一种新型方法，具有甲醇进料浓度较低（<10%），反应温度相对较低（~280 ℃），甲醇转化率高达100%、甲醛选择性高（~92%）的优点，在经济上更具优势，因而已经逐渐受到全世界学术界和工业界专家的关注。铁钼法的核心是主要成分为Fe₂(MoO₄)₃和过量MoO₃的，具有高活性和高选择性的钼酸铁催化剂（简称铁钼催化剂）。

本文采用共沉淀法制备铁钼催化剂前体，采用SEM、TEM、XRD等表征手段深入研究了各关键工艺参数、MoO₃相以及成型手段对催化剂结构、形貌、反应热效应及催化性能的影响规律，获得最佳生产工艺条件和技术路线。主要发现和结论如下。

（1）通过正交实验考察共沉淀法制备铁钼催化剂过程，研究沉淀pH、母液浓度、老化温度、投料钼铁比对催化剂结构、形貌、反应热效应及催化性能的影响，获得上述因素的最优水平，结果表明铁钼催化剂粉体以共沉淀法生产时，控制沉淀温度在90 ℃，pH在2.0，投料钼铁比在2.5时所得催化剂晶体生长良好，粒径均匀，催化性能最好。

（2）对MoO₃的作用进行了探究，结果表明，与传统观点不同，催化剂中MoO₃不仅对催化剂寿命产生影响，其晶粒尺寸对催化剂活性同样具有重要影响，MoO₃尺寸为52.2 nm时，甲醛收率可达89%。

（3）工业用铁钼催化剂通常需要压片成型，成型后的铁钼催化剂需要具有一定的机械强度，以适应工业反应器高温、高空速的工况，本文对铁钼催化剂粉体预处理及成型进行了研究，结果表明，为满足成型要求，需要控制粉体形状、大小及含水量在15%，当添加2%硅溶胶作粘合剂、2%硬脂酸作润滑剂时，制得的催化剂强度>200 N，满足工业用甲醇氧化制甲醛铁钼催化剂要求。

ABSTRACT

Formaldehyde (CH₂O) is a major chemical with an important position in the chemical industry. It is one of the basic raw materials in the chemical industry. Selective oxidation of methanol (CH₃OH) to prepare formaldehyde is currently a commonly used method in production. Among them, catalysts are key factors in controlling reaction efficiency and final product quality. The iron-molybdenum method is a novel method for the selective oxidation of methanol to formaldehyde using iron molybdate as a catalyst. It has the advantages of low methanol feed concentration (<10%), relatively low reaction temperature (~280 °C), high methanol conversion rate of up to 100%, and high selectivity for formaldehyde (~92%). It has economic advantages and has gradually attracted the attention of experts in academia and industry worldwide. The core of the iron-molybdenum method is a high-activity and high-selectivity iron molybdate catalyst (referred to as iron-molybdenum catalyst) with the main components of Fe₂(MoO₄)₃ and excess MoO₃.

In this paper, the preparation of iron-molybdenum catalyst precursor by co-precipitation method was investigated, and the effects of various key process parameters, MoO₃ phase, and forming methods on the structure, morphology, reaction heat effect, and catalytic performance of the catalyst were deeply studied using SEM, TEM, XRD, and other characterization methods. The optimal production process conditions and technical route were obtained. The main findings and conclusions are as follows.

(1) Through orthogonal experiments, the preparation process of iron-molybdenum catalysts by co-precipitation was investigated, and the effects of precipitation pH, mother liquor concentration, aging temperature, and feed molybdenum-iron ratio on the structure, morphology, reaction heat effect, and catalytic performance of the catalysts were studied. The optimal levels of the above factors were obtained. The results showed that when the iron-molybdenum catalyst powder was produced by co-precipitation, the precipitation temperature was controlled at 90 °C, the pH was 2.0, and the feed molybdenum-iron ratio was 2.5. The resulting catalyst crystals grew well with uniform particle size and the best catalytic performance.

(1) Through orthogonal experiments, the effects of precipitation pH, mother liquor concentration, aging temperature, and Fe/Mo ratio on the structure, morphology, reaction heat effect, and catalytic performance of the catalyst prepared by co-precipitation were investigated. The optimal levels of the above factors were obtained. The results showed that when the iron-molybdenum catalyst powder was produced by co-precipitation, the crystal growth of the catalyst was good when the precipitation temperature was controlled at 90 °C, the pH was 2.0, and the Fe/Mo ratio was 2.5. The particle size was uniform and the catalytic performance was the best.

(2) The role of MoO₃ was explored. The results showed that, contrary to conventional views, MoO₃ in the catalyst not only affected the lifetime of the catalyst, but also had a significant impact on the activity of the catalyst. When the size of MoO₃ was 52.2 nm, the yield of formaldehyde reached 89%.

(3) Industrial iron-molybdenum catalysts usually require pressing and forming, and the formed iron-molybdenum catalysts need to have certain mechanical strength to adapt to the high temperature and high space velocity conditions of industrial reactors. This article studies the pretreatment of iron-molybdenum catalyst powder and the formation of iron-molybdenum catalyst. The results show that in order to meet the forming requirements, it is necessary to control the shape, size, and moisture content of the powder to 15%. When adding 2% silica sol as a binder and 2% stearic acid as a lubricant, the strength of the catalyst produced is >200 N, meeting the requirements of industrial methanol oxidation to formaldehyde iron-molybdenum catalysts.

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