Application Of Porous Materials For Catalytic Oxidation Of Toluene In Liquid Phase

Here，an in situ method to synthesize acid-functionalized mesoporous silicaswith sulfonic groups is proposed. As-synthesized SBA-15without calcination toremove the non-ionic P123（EO20PO70EO20） template was treated by H2SO4via athermal process. The carbonization of the non-ionic P123resulted in carbon specieswhich could be dispersed on the outer and inner surface of SBA-15. The resultantmaterials which were characterized by N₂sorption, powder X-Ray Diffraction（XRD）, Transition Electron Microscopy （TEM） and Scanning Electron Microscopy（SEM） were a type of sulfonic acid-functionalized mesoporous silicas with highlyordered2D hexagonal mesostructure. The results of X-ray PhotoelectronSpectroscopy （XPS）, Fourier Transform-Infrared Spectroscopy （FT-IR） andacid-base titration experiment indicated the presence of sulfonic and carboxylicgroups in the resultant materials. The concentration of S atoms was determined byICP. Furthermore, the impact of various temperature treatments on the textualproperites and the catalytic performance of the resultant materials were alsoinvestigated. These acid-functionalized materials were employed as catalysts for theesterification of acetic acid with butyl alcohol and exhibited different catalyticactivity. The comparative investigation on the recycling experiments reveals thedifferent performance of the catalysts with immobilized sulfonic groups. Moreover,this hydrothermal treatment using H2SO4solution was employed to synthesizesulfonic acid-functionalized composite. Carbonization of glucose, sulfonation ofcarbonized glucose and deposition of amorphous carbon occurred on the surface ofmesoporous silicas. The resultant composite, investigated by powder XRD, lowtemperature N₂sorption and FT-IR, possessed well defined mesostructure.Porous materials, including HZSM-5, NaZSM-5, HBeta, TS-1, ETS-4, SBA-15,acid-functionalized SBA-15and mesostructured composite with acid functionalgroups, were used as catalysts for the oxidation of toluene. Meanwhile, oxidation ofbenzyl alcohol was also investigated. SBA-15, mesostructured composite andHZSM-5exhibited lower catalytic activity for solvent-free oxidation of benzyl alcohol with oxygen. Acid-functionalized SBA-15performed well in the solvent-freeoxidation of benzyl alcohol with oxygen due to the immobilization of sulfonic groups.And Pd/C/SBA-15exhibited moderate activity for solvent-free oxidation of benzylalcohol with high selectivity for the benzaldehyde. However, all these catalystsmentioned above exhibited poor catalytic activity for the solvent-free oxidation oftoluene with oxygen. On the other hand, we proposed an effective heterogeneouscatalytic system employing aqueous media for the oxidation of toluene. It was foundthat alkali-treated zeolites could efficiently catalyze oxidation of toluene with H2O2inaqueous media. Through optimizing the experimental conditions, alkali-treatedHZSM-5exhibited good catalytic activity for toluene oxidation in only5h at a lowtemperature （below373K）:32.0%conversion of toluene with selective formation of25.0%benzaldehyde,20.8%benzyl alcohol and27.5%benzoic acid. A probableredox mechanism for toluene oxidation catalyzed by alkali-treated zeolites in aqueousmedia was proposed in this work.No heavy metals or their oxides were employed in the synthesis of catalyst andno additives were used in this catalytic system. In the absence of heavy metals andadditives, this catalytic system is simple, efficient and environment-friendly.Furthermore, the mild reaction conditions avoided the formation of coke on thecatalyst. And the results of recycling experiment demonstrated that alkali-treatedHZSM-5zeolite was a durable heterogeneous catalyst for the liquid-phase oxidationof toluene. In conclusion, this catalytic system enriches the common processes oftoluene oxidation and further investigation based on these preliminary results mightintroduce new insight into the catalytic mechanism of toluene oxidation. Moreover,alkali-treated zeolites are promising catalysts for the oxidation of toluene in theindustrial application.