The influences of Al species and Ti species on the catalytic epoxidation over Si/Ti-pillared MCM-36 synthesized from MCM-22

Abstract

A novel mesopore silica-aluminium material, i.e., Si/Ti-MCM-36 derivatives were prepared with Si/Ti mixed oxide as a pillar. The influences of acidity from Al species and the coordination state of Ti species on the catalytic cylcohexene epoxidation with t-butylhydroperoxide (TBHP) as the oxidant were investigated. The mesoporous structures were confirmed by XRD and N 2 ads/desorption experiment. The acidity and surface polarity were characterized by NH 3 -TPD, 27 Al 2D MQ MAS NMR and 29 Si MAS NMR. The Ti coordination state was identified with UV-Vis spectra. By using 27 Al 2D MQ MAS NMR technique, the Al species from the different eight crystallographically T (Si, Al) positions of MWW zeolite were identified, which are associated with bridging hydroxyl groups such as the Brønsted acid site. It was found that the Si/Ti-MCM-36 samples, whether with tetrahedrally (T d ) or octahedrally (O h ) coordinated state Ti species, are all inactive for the cyclohexene epoxidation. A further acid treatment of the Si/Ti-MCM-36 samples can greatly expel Al species from the MWW structure, which largely decrease the acidity and transfer the acid-catalyzed decomposition of t-butylhydroperoxide to Ti catalyzed cyclohexene epoxidation. It shows that not only the amount of Al species but also their framework crystallographic positions have a great influence on the epoxidation activity. Furthermore, the grafting of the tetra-isopropoxide on the acid treated Si/Ti-MCM-36 can increase its hydrophobicity and epoxidation activity. Moreover, the T d TiO 4 in the units has been confirmed to be the most active site for the epoxidation reaction.

Heteroatomic Zn‐MWW Zeolite Developed for Catalytic Dehydrogenation Reactions: A Combined Experimental and DFT Study

“…The overall acidity of Zn-MWWw as compared with that of MCM-22 by using NH 3 temperature-programmedd esorption (TPD) techniques, ass hown in Figure 5. As expected, ITQ-1 shows no significant NH 3 desorption during NH 3 -TPD analysis, indicating negligible acidity.T he NH 3 -TPD profile of MCM-22 is consistentw ith the one reported by Jin et al [27] The total NH 3 desorption is 571 mmol g À1 over Zn-MWW, which is higher than that on MCM-22 (440 mmol g À1 ). To get ad eeper insighti nto their acid properties, the NH 3 -TPD patterns were fitted with Gaussianp eaks and the resultsa re listed in Ta ble 2.…”

Layer like porous materials with hierarchical structure

“…The obtained pillared MCM-22 materials showed BET area above 700 m 2 /g and after acid treatment became active for cyclohexene epoxidation. 187 As said at the beginning the concept of pillaring of layered materials started with intercalation of organic compounds but subsequent effort was focused on preparation of thermally stable inorganic pillars. As diverse systems and compositions were being explored later on the studies were again extended to pillaring of layered silicates with organic pillars.…”

A Lamellar MWW Zeolite With Silicon and Niobium Oxide Pillars: A Catalyst for the Oxidation of Volatile Organic Compounds

“…MCM‐36 with alumina‐magnesia as mixed pillars was the first example of this approach and had pore diameters of 2–4 nm, and this concept was extended to other mixed pillars with BaO‐Al 2 O 3 , Al 2 O 3 ‐SiO 2 , MgO‐Al 2 O 3 ‐SiO 2 , and BaO‐Al 2 O 3 ‐SiO 2 . A pillared MWW zeolite with Si/Ti as mixed pillars was reported as catalysts for epoxidation of cyclooctene . Recently, a pillared MWW with niobiosilicate was reported, and the materials were active for cyclohexene oxidation and methylene blue discoloration with hydrogen peroxide .…”