Janiszewska Ewa, Held Agnieszka, Nowińska Krystyna, Kowalak Stanisław
Adam Mickiewicz University, Faculty of Chemistry Umultowska 89b 61614 Poznan Poland
RSC Adv. 2019 Feb 6;9(9):4671-4681. doi: 10.1039/c8ra10171j. eCollection 2019 Feb 5.
V-containing silica SBA-3 mesoporous catalysts were prepared by means of one-pot hydrothermal procedure with NHVO or VOSO as vanadium precursors under various acidic medium of the reaction mixture (pH < 1, 2.2 or 3.1). The combined spectral techniques (DR UV-vis, FTIR, EPR) as well H-TPR allowed to determine the nature of vanadium species in the studied samples. A successful incorporation of vanadium into the structure of silica SBA-3 was attained for the samples with low V content (<1 wt%), whereas the V-rich samples ( >5 wt%) exhibited the presence of isolated vanadium and also of polynuclear surface species. The resulting V-bearing samples contain the Brønsted and Lewis acidic centres evidenced by FTIR spectra of adsorbed pyridine and by catalytic activity for 2-propanol decomposition and cumene cracking. Ammonia TPD allowed to estimate the number and strength of acid sites in regards to the vanadium content. Propene oxidation with NO revealed noticeable activity of the synthesised V-SBA-3 samples in epoxidation reaction. On the basis of TOF analysis indicating the activity of particular vanadium ions it seems that not all of the introduced V atoms take part in the formation of mild electrophilic oxygen species responsible for propene oxide formation.
含钒二氧化硅SBA - 3介孔催化剂是通过一锅水热法制备的，以NHVO或VOSO作为钒前驱体，在反应混合物的各种酸性介质（pH < 1、2.2或3.1）下进行。结合光谱技术（DR紫外 - 可见光谱、傅里叶变换红外光谱、电子顺磁共振）以及H - TPR能够确定所研究样品中钒物种的性质。对于低钒含量（<1 wt%）的样品，钒成功地掺入了二氧化硅SBA - 3的结构中，而高钒含量（>5 wt%）的样品则显示出存在孤立的钒以及多核表面物种。所得的含钒样品含有通过吸附吡啶的傅里叶变换红外光谱以及对2 - 丙醇分解和异丙苯裂解的催化活性所证明的布朗斯特和路易斯酸性中心。氨程序升温脱附能够估计相对于钒含量的酸位点数量和强度。用NO进行丙烯氧化显示合成的V - SBA - 3样品在环氧化反应中具有明显的活性。基于表明特定钒离子活性的TOF分析，似乎并非所有引入的V原子都参与了负责环氧丙烷形成的温和亲电氧物种的形成。
