碱性添加剂在钛硅分子筛/H2O2催化丙烯环氧化反应中的作用

考察了反应溶液中碱性添加剂{氨水（NH₄OH）、氢氧化钠（NaOH）、碳酸钠（Na₂CO₃）、碳酸铵(NH₄)₂CO₃]和四甲基氢氧化铵（TMAOH）}及其浓度对钛硅分子筛（TS-1）催化丙烯环氧化反应性能的影响，并采用紫外拉曼光谱（UV-Raman）与气相色谱（GC）联用原位分析（Raman-GC）碱性添加剂的作用机理。结果表明：反应体系中添加碱性添加剂可有效改善TS-1催化丙烯环氧化反应的选择性。不同碱性添加剂对TS-1催化丙烯环氧化活性和稳定性影响不同，NaOH、Na₂CO₃和TMAOH的添加造成催化活性和稳定性降低。NH₄OH或(NH₄)₂CO₃作为添加剂改善环氧化反应选择性的同时提高了反应稳定性，其中以(NH₄)₂CO₃效果最佳。添加(NH₄)₂CO₃浓度为8.0×10^-4mol/L时，TS-1催化丙烯环氧化在固定床反应器上连续运行336h时，X(H₂O₂)仍保持在90%以上。原位Raman-GC分析发现，反应体系中NH₄OH和(NH₄)₂CO₃添加可加快反应活性中间体Ti-OOH(η²)基团的生成，促进反应产物从活性中心快速扩散，从而提高丙烯环氧化反应选择性和稳定性。

Effect of basic additive in feedstock on propylene epoxidation catalyzed by TS-1/H2O2

NH₄OH, NaOH, Na₂CO₃, (NH₄)₂CO₃ and TMAOH were selected as the basic additive in the feedstock of propylene epoxidation reaction and their effects on the performance of TS-1 catalysis were evaluated by in-situ Raman spectrometry-gas chromatography. The experimental results suggested that the performance of the TS-1 catalyst was influenced significantly by the composition of feedstock. However, the presence of NH₄OH or (NH₄)₂CO₃ at a suitable concentration could improve the catalytic activity, selectivity and the stability of the TS-1 catalyst. When (NH₄)₂CO₃ concentration in feedstock was 8.0×10^-4mol/L, the best catalytic performance was obtained. The X(H₂O₂) still remained above 90% after a long-term run of 336h in a fixed-bed reactor. In-situ Raman-GC showed that the basic additive promoted the formation of the reactive intermediates Ti-OOH(η²) and accelerated the diffusion of reaction products from active centers.