Epoxidation of 1-octene under harsh tail-end conditions in a flow reactor I: a comparative study of crystalline vs. amorphous catalysts†,Reaction Chemistry & Engineering

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Epoxidation of 1-octene under harsh tail-end conditions in a flow reactor I: a comparative study of crystalline vs. amorphous catalysts†
Reaction Chemistry & Engineering ( IF 3.4 ) Pub Date : 2017-07-26 00:00:00 , DOI: 10.1039/c7re00076f
Martina Aigner _{1,

2,

3,

4} , Nicolás Andrés Grosso-Giordano _{1,

2,

3,

4} , Alexander Okrut _{1,

2,

3,

4} , Stacey Zones _{4,

5,

6} , Alexander Katz _{1,

2,

3,

4}

Affiliation

Amorphous silica versus crystalline delaminated-zeolite catalysts consisting of grafted Ti(IV) Lewis-acid active sites were investigated from the perspective of 1-octene olefin epoxidation with ethylbenzene hydroperoxide (EBHP) as oxidant. Reactions were performed at conditions of temperature and concentrations of organic hydroperoxide and inhibitors (epoxide product and alcohol co-product) that mimic the harsh conditions found at the tail-end of the flow reactor for industrial propylene-oxide (PO) synthesis, where there is a current need to improve activity and selectivity, because of deactivation. Catalyst synthesis was performed by grafting a Ti-alkoxide precursor onto framework vacancies (“silanol nests”) of the delaminated zeolite UCB-4, as well as onto amorphous SiO₂. Both catalysts were characterized by powder X-ray diffraction (PXRD), nitrogen physisorption at 77 K, and UV-visible spectroscopy before and after catalysis. Experiments at different conversions were performed, and show that crystalline Ti-UCB-4 exhibits a ∼9% higher average selectivity (73% versus 64%) and greater conversion, stability, and robustness upon increasing time on stream relative to amorphous Ti–SiO₂. UV-vis spectra are discussed for fresh, spent, and spent/calcined materials and demonstrate that Ti sites in Ti-UCB-4 exist as isolated grafted complexes with four-fold coordination to the zeolite framework, whereas Ti–SiO₂ consists of grafted Ti-sites on the silica surface, some of which are isolated but a dominant proportion of which are TiO₂ oligomers. The observed increased stability of the crystalline catalyst under tail-end reactor conditions is attributed to the surface pockets of the crystalline material, in which Ti is grafted.

中文翻译：

1-辛烯在苛刻的尾端条件下在流动反应器中的环氧化反应I：结晶催化剂与无定形催化剂的比较研究†

从1-辛烯烯烃环氧化用乙苯氢过氧化物（EBHP）作为氧化剂的角度研究了由接枝的Ti（IV）路易斯酸活性位组成的无定形硅石对结晶脱层沸石催化剂。反应是在一定温度和有机过氧化氢和抑制剂（环氧产物和醇副产物）的浓度条件下进行的，这些条件模拟了在工业合成环氧丙烷（PO）合成用流动反应器尾部发现的苛刻条件。由于失活，目前是提高活性和选择性的需要。通过将钛醇盐前体接枝到分层沸石UCB-4的骨架空位（“硅烷醇巢”）以及无定形SiO上来进行催化剂合成₂。两种催化剂的特征均在于粉末X射线衍射（PXRD），77 K下的氮物理吸附以及催化前后的紫外可见光谱。进行了不同转化率的实验，结果表明，相对于无定形Ti-SiO，结晶Ti-UCB-4的平均选择性提高了约9％（73％比64％），并且转化率，稳定性和耐用性随流逝时间的延长而提高。₂。讨论了新鲜，废料和废料/煅烧材料的紫外可见光谱，结果表明Ti-UCB-4中的Ti位点是作为孤立的接枝复合物存在的，与沸石骨架具有四重配位，而Ti-SiO₂由二氧化硅表面的接枝钛位点组成，其中一些是孤立的，但主要部分为TiO ₂低聚物。在尾部反应器条件下观察到的结晶催化剂稳定性的提高归因于其中接枝了Ti的结晶材料的表面囊。

更新日期：2017-07-26

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