关于对丙烯氧化催化剂的研究和分析

对丙烯酸催化剂进行的性能试验,获得了最佳的工艺条件：第一反应器盐浴温度：320±10℃;丙烯空速95 hr-1,丙烯转化率在98%以上,第二反应器盐浴温度260±10℃,丙烯醛空速96.5 hr-1,丙烯醛转化率在99.58%以上。     

干燥方式对丙烯醛部分氧化制丙烯酸催化剂的影响

钼钒钨复合金属氧化物是典型的丙烯醛部分氧化制丙烯酸催化剂,铜、锑是良好的助剂.干燥方式对催化剂性能有较大影响.评价结果表明,喷雾干燥得到无定型的催化剂粉末,较结晶干燥方式具有更好的催化活性和选择性,适应的温度范围较宽.采用XRD、SEM和EDX方法对催化剂进行了表征,表明喷雾干燥所得样品元素分布更均匀.     

丙烯醛水合催化剂的研究进展

介绍了国内外关于丙烯醛水合制备3-羟基丙醛催化剂的研究进展。重点对多种类催化剂催化效果进行了介绍,并对其工业化应用可行性进行了评价及比较。     

丙烯醛温和液相反应制备3-甲基吡啶工艺

以丙烯醛为原料,通过单因素实验,建立了优化的温和液相反应合成3-甲基吡啶的优化工艺条件：以乙二醇单丁醚为溶剂,反应温度140℃,料液比n(丙烯醛):n(乙二醇单丁醚)=1:33,n(丙烯醛):n(乙酸铵)=1:8,w(丙烯醛正丁酸溶液)=8%,m(丙烯醛):m(SO24-/TiO2-HZSM-5催化剂)=1:1.4。在优化条件下,实现了丙烯醛转化率100%,3-甲基吡啶选择性49.92%。     

超稳Y型分子筛的骨架硅铝比对甘油气相脱水反应的影响

以铵交换和高温水热处理法制备了不同硅铝比的超稳Y型分子筛（USY）,利用X射线衍射、扫描电镜、氮气吸附脱附和吡啶红外等技术对USY进行了表征。以USY为催化剂,考察了USY的骨架硅铝比对气相甘油脱水制丙烯醛的影响。X射线衍射和扫描电镜结果表明,铵交换和高温水热处理只是提高USY的硅铝比,相对结晶度略有降低,而对Y型分子筛的结构和形貌没有影响。氮气吸附-脱附和吡啶红外结果表明,随USY骨架SiO₂/Al₂O₃比提高,总酸量和B酸酸量逐渐降低,L酸酸量有所增多,介孔孔体积和平均孔径有所增大。气相甘油脱水反应结果表明,催化剂织构性质对甘油转化率和丙烯醛选择性的影响大于酸性的影响,因而SiO₂/Al₂O₃比为29的USY催化剂的反应性能最好,甘油转化率和丙烯醛收率分别达到了84.5%和51.8%。     

1,3-丙二醇合成工艺研究进展

介绍了国内外1,3-PDO的合成工艺及其最新研究进展,较为详细的讨论了环氧乙烷羰基化法、丙烯醛水合法、微生物发酵法和醇醛缩合法的合成路线、工艺条件、催化剂等,并对其进行了综合比较,展望了今后的研究发展方向。     

Unbalance between Pyridine Nucleotide Cofactors in The SOD1 Deficient Yeast Saccharomyces cerevisiae Causes Hypersensitivity to Alcohols and Aldehydes

Alcohol and aldehyde dehydrogenases are especially relevant enzymes involved in metabolic and detoxification reactions that occur in living cells. The comparison between the gene expression, protein content, and enzymatic activities of cytosolic alcohol and aldehyde dehydrogenases of the wild-type strain and the Δsod1 mutant lacking superoxide dismutase 1, which is hypersensitive to alcohols and aldehydes, shows that the activity of these enzymes is significantly higher in the Δsod1 mutant, but this is not a mere consequence of differences in the enzymatic protein content nor in the expression levels of genes. The analysis of the NAD(H) and NADP(H) content showed that the higher activity of alcohol and aldehyde dehydrogenases in the Δsod1 mutant could be a result of the increased availability of pyridine nucleotide cofactors. The higher level of NAD⁺ in the Δsod1 mutant is not related to the higher level of tryptophan; in turn, a higher generation of NADPH is associated with the upregulation of the pentose phosphate pathway. It is concluded that the increased sensitivity of the Δsod1 mutant to alcohols and aldehydes is not only a result of the disorder of redox homeostasis caused by the induction of oxidative stress but also a consequence of the unbalance between pyridine nucleotide cofactors.     

Peroxo salts as initiators of vinyl polymerization: Polymerization of acrolein initiated by potassium peroxodiphosphate

Kinetic studies were made on the polymerization of acrolein initated by potassium peroxodiphosphate (PP) in aqueous solution, in the presence and absence of Ag⁺ ions. The rate of polymerization was found to depend on [M]^3/2 (M = monomer) and was independent of both [PP] and [Ag⁺]. The overall activation energy was calculated to be 4.8 kcal mol⁻¹. A mechanism involving termination by PO^2-₄ radicals is proposed and discussed.     

Mode of action of oxidation‐active centres in Mo–V mixed oxides on the partial oxidation of an unsaturated aldehyde

The mode of action of the oxidation‐active centres in Mo–V mixed oxides on the selective oxidation of an unsaturated aldehyde was investigated by non‐steady‐state methods. Various oxidation‐active centres, differing in activity and selectivity, were identified by non‐steady‐state methods. In addition, the influence of the crystallinity of the Mo–V mixed oxides on the activity and selectivity properties were investigated. It was shown that, in contrast to crystalline samples, only X‐ray‐amorphous Mo–V mixed oxides contained selective oxidation centres. The measurements were used to derive a model based on the interaction of active centres with various redox properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Multifunctionality of Active Centers in (Amm)oxidation Catalysts: From Bi–Mo–O x to Mo–V–Nb–(Te, Sb)–O x

Catalytic centers in selective (allylic) oxidation and ammoxidation catalysts are multimetallic and multifunctional. In the historically important bismuth molybdates, used for propylene (amm)oxidation, they are composed of (Bi³⁺)(Mo⁶⁺)₂ complexes in which the Bi³⁺ site is associated with the -H abstraction and the (Mo⁶⁺)₂ site with the propylene chemisorption and O or NH insertion. An updated reaction mechanism is presented. In the Mo–V–Nb–Te–O _x systems, three crystalline phases (orthorhombic Mo_7.5V_1.5NbTeO₂₉, pseudohexagonal Mo₆Te₂VO₂₀, and monoclinic TeMo₅O₁₆) were identified, with the orthorhombic phase being the most important one for propane (amm)oxidation. Its active centers contain all necessary key catalytic elements (2V⁵⁺/Mo⁶⁺, 1V⁴⁺/Mo⁵⁺, 2Mo⁶⁺/Mo⁵⁺, 2Te⁴⁺) for this reaction wherein a V⁵⁺ surface site (V⁵⁺ = O ⁴⁺V–O) is associated with paraffin activation, a Te⁴⁺ site with -H abstraction once the olefin has formed, and a (Mo⁶⁺)₂ site with the NH insertion. Four Nb⁵⁺ centers, each surrounded by five molybdenum octahedra, stabilize and structurally isolate the catalytically active centers from each other (site isolation), thereby leading to high selectivity of the desired acrylonitrile product. A detailed reaction mechanism of propane ammoxidation to acrylonitrile is proposed. Combinatorial methodology identified the nominal composition Mo_0.6V_0.187Te_0.14Nb_0.085O _x for maximum acrylonitrile yield from propane, 61.8% (86% conversion, 72% selectivity at 420 °C). We propose that this system, composed of 60% Mo_7.5V_1.5NbTeO₂₉, 40% Mo₆Te₂VO₂₀, and trace TeMo₅O₁₆, functions with a combination of compositional pinning of the optimum orthorhombic Mo_7.5V_1.5±x Nb_1±y Te_1±z O_29± phase and symbiotic mop-up of olefin intermediates through phase cooperation. Under mild reaction conditions, a single optimum orthorhombic composition might suffice as the catalyst; under demanding conditions this symbiosis is additionally required. Improvements in catalyst performance could be attained by further optimization of the elemental distributions at the active catalytic center of Mo_7.5V_1.5NbTeO₂₉, by promoter/modifier substitutions, and incorporation of compatible cocatalytic phases (preferably epitaxially matched). High-throughput methods will greatly accelerate the rational catalyst design processes.