共查询到17条相似文献,搜索用时 281 毫秒
1.
酸性中心对复合氧化物催化苯酚羟基化反应的影响 总被引:2,自引:0,他引:2
铁基复合氧化物催化苯酚羟基化反应具有明显的诱导期,适当引入酸性中心,在氧化还原活性位的共同存在下,可以迅速缩短羟基化反应的诱导期;酸性中心弱或没有采用酸改性的复合氧化物催化剂,对苯酚羟基化反应催化作用活性低,催化剂用量大,反应诱导期不稳定。乙酸、乙酸酐等有机弱酸可以直接加入羟基化反应体系。对复合氧化物催化剂进行后处理改性,引入适当的酸性中心,有助于提高催化剂的活性,缩短甚至消除羟基化反应诱导期,避免由于未反应过氧化氢的积累增加反应器运行的风险,提高过氧化氢有效利用率和目标产物选择性。将5.3g苯酚、0.051g催化剂、过氧化氢与苯酚的物质的量比为0.33,在65℃下,于10.6g溶剂水中反应,时间为30min,反应诱导期仅5min,苯酚转化率达21.2%,苯二酚选择性为92.9%,过氧化氢有效利用率为59.6%。分析了直接加入酸性中心和对复合氧化物催化剂进行酸改性所带来的问题,推测了苯酚羟基化反应的机理。 相似文献
2.
Hβ沸石修饰的复合氧化物对苯酚羟基化反应的催化作用 总被引:1,自引:0,他引:1
采用不同硅铝比的Hβ沸石对铁基复合金属氧化物催化剂进行了修饰,发现复合氧化物催化体系中掺入适量具有特定结构的Hβ沸石,可以提高催化剂的活性,缩短甚至消除羟基化反应诱导期,避免由于未反应过氧化氢的积累增加反应器运行的风险,提高过氧化氢有效利用率和目标产物选择性。但过多的Hβ沸石导致苯酚和苯二酚缩合生成不溶于水的焦油,降低了羟基化反应的目标产物选择性。比较合适的修饰用Hβ沸石包括Hβ-80、Hβ-63和Hβ-48。比较好的Hβ-80沸石掺入质量分数为7%,以7% Hβ沸石修饰的Fe-Cu-Sn-Zn-O/γ-Al2O3复合氧化物作催化剂,反应温度65 ℃、反应时间30 min、苯酚5.3 g、溶剂水10.0 g、m(苯酚)∶m(催化剂)=294、n(过氧化氢)∶n(苯酚)=0.33时,反应诱导期不到1 min,苯酚转化率22.3%,苯二酚选择性91.9%,过氧化氢有效利用率62.1%。 相似文献
3.
4.
一种高性能的苯酚羟基化用复合氧化物催化剂 总被引:2,自引:0,他引:2
用Hβ沸石对复合氧化物进行修饰和改性,制得一种高性能苯酚羟基化用复合氧化物催化剂Fe Hβ80〔w(Hβ) =7%〕。以Fe Hβ80做催化剂,对羟基化反应工艺条件进行了优化,优化的反应工艺条件为:反应温度65~70℃,反应时间0 25~0 5h,m(苯酚) /m(催化剂) =294~883,n(苯酚) /n(H2O2 ) =3 00~5 78,m(苯酚) /m(水) =0 43~0 91。以Fe Hβ80作催化剂,去离子水为溶剂,反应温度65℃,反应时间30min,苯酚5 3g,m(苯酚) /m(催化剂) =294,n(苯酚) /n(H2O2 ) =3 00,溶剂水10 0g,反应结果表明,羟基化反应诱导期不到1min,苯酚转化率22 3%,苯二酚选择性91 9%,过氧化氢有效利用率62 1%。与Fe Cu Sn Zn O/γAl2O3、Fe Mg O/γAl2O3 和TS分子筛等典型苯酚羟基化用催化剂相比较,由于Hβ沸石能为复合氧化物催化剂提供合适的酸性中心,从而缩短了苯酚羟基化反应诱导期,提高了催化活性和目标产物选择性,降低了过氧化氢在反应器中积累所带来的风险。Fe Hβ80催化剂用量仅为TS分子筛的1 /29 4(质量比), 但羟基化反应诱导期仅1min(TS分子筛为120min),证明Fe Hβ80是一种高性能的苯酚羟基化用催化剂。 相似文献
5.
6.
含铁过渡金属类复合氧化物对苯酚过氧化氢羟化的催化作用的研究 总被引:5,自引:0,他引:5
对含铁过渡金属类复合氧化物催化剂CF-16对苯酚羟基化反应的催化作用进行了研究,考察了反应温度、催化剂用量、双氧水用量、酸介质等因素对催化性能的影响。实验结果表明,当催化剂/苯酚(重量比)为0.05,过氧化氢/苯酚(摩尔比)为0.49,反应温度为60~70℃,反应时间0.5小时,苯酚转化率大于26%,苯二酚选择性大于94%。相对钛硅分子筛TS-1、TS-2而言,含铁复合金属类氧化物催化剂价格低廉, 相似文献
7.
8.
9.
催化苯直接羟基化是开发绿色苯酚生产新技术的高原子经济性的挑战性课题,但该工艺存在芳香C-H键难活化、产物酚的选择性较低等问题,其中高效催化剂的研制是核心问题之一。根据含铁催化剂独特的化学结构和催化性能,本文从配合物均相催化剂、仿生催化剂、负载型非均相催化剂等方面综述了含铁催化剂催化苯直接羟基化制备苯酚的研究进展,并着重介绍了Fenton体系和仿生催化体系的反应机理。分析表明,以氧化物及天然矿物作为载体的含铁催化剂合成简单,活性高,有较大的研究及工业开发价值。此外,研究催化机理对设计合成高效苯羟基化的催化剂具有指导意义。 相似文献
10.
11.
Pyridine(Py)-modified Keggin-type mono-vanadium-substituted heteropoly acids (Py n PMo11V, n = 1–4) were prepared by a precipitation method as organic/inorganic hybrid catalysts for direct hydroxylation of benzene to phenol in a pressured batch reactor and their structures were characterized by FT-IR. Among various catalysts, Py4PMo11V exhibited the highest catalytic activity (yield of phenol 9.0%) with the high selectivity for phenol, without observing the formation of catechol, hydroquinone and benzoquinone in the reaction with 80 vol% aqueous acetic acid, molecular oxygen and ascorbic acid used as the solvent, oxidant and reducing reagent, respectively. The influences of the reaction temperature, the pressure of oxygen, the amount of ascorbic acid, the amount of catalyst, and the reaction time on the yield of phenol were investigated to obtain the optimal reaction conditions for phenol formation. Pyridine can greatly promote the catalytic activity of the Py-free catalyst (H4PMo11VO40), mostly because the organic π electrons in the hydrid catalyst may extend their conjugation to the inorganic framework of heteropoly acid and thus dramatically modify the redox properties. 相似文献
12.
13.
14.
Attrition properties of several oxide supports and precipitated iron-based F–T catalyst (100Fe/3Cu/4K/16SiO2 in parts by weight) were evaluated using ultrasound irradiation test and stirred tank slurry reactor (STSR) test under non-reactive conditions. Attrition by fracture and erosion of the iron-based catalyst was small in both types of tests and its overall attrition strength was better than that of the alumina and silica supports, which were evaluated under the same conditions. Also, attrition studies with four iron-based F–T catalysts were conducted under reaction conditions in the STSR. Catalyst of similar composition, as that used in non-reactive studies, prepared by spray drying technique had the highest attrition strength among all catalysts tested. 相似文献
15.
利用可再生清洁能源——太阳能,将CO2转化为一氧化碳、甲烷、甲醇等,因同时具有提供可持续燃料和解决全球变暖问题的潜力而受到越来越多的关注。铁基材料因具有金属/半导体的特性和独特的电子结构,在光催化还原CO2领域具有广阔的应用潜力。基于此,各种具有高催化活性的铁基催化剂已经被设计来提高光催化还原CO2的效率。概述了近年来铁基催化剂在光催化还原二氧化碳中的研究进展,对它们的结构特征和催化活性进行了阐述和比较,最后总结了铁基催化剂在光催化还原CO2领域中待解决的问题,并展望了未来发展的方向。 相似文献
16.
17.
Atsutaka Kunai Tomoyuki Kitano Yasushi Kuroda Jiang Li-Fen Kazuo Sasaki 《Catalysis Letters》1990,4(2):139-144
Usefulness of silica supported palladium catalysts applied for the hydroxylation reaction of benzene under ambient conditions has been demonstrated. Two types of catalyst, Pd alone and CuPd composite catalysts both being supported on silica, were found to behave in remarkably different ways which are dependent also on the mode of reactant gas feeding. The Pd single component catalyst is powerful when hydrogen and oxygen are simultaneously present in the reacting system and produces phenol almost exclusively. On the other hand, the composite catalyst can be used irrespective of the mode of gas feeding. If quinones are desired, the use of the composite catalyst is recommended but if phenol is desired the Pd single component catalyst seems to be advantageous. 相似文献