Solid Acid Catalysts: Modification of Acid Sites and Effect on Activity and Selectivity Tuning in Various Reactions

Abstract

The effects of acidity and variation in concentration of acid sites of dodecatungstophosphoric acid (DTP), supported DTP and montmorillonite-K catalysts were studied for various organic reactions such as the hydroxyalkylation of phenols to bisphenols, intramolecular rearrangement of benzyl phenyl ether (BPE) to 2-benzyl phenol (2-BP) and selective cleavage of tert-butyldimethylsilyl (TBDMS) ether into the corresponding alcohol. Both dodecatungstophosphoric acid (DTP) impregnated on silica (SiO 2 ) and montmorillonite catalysts showed the highest catalyst activity with 90-95% selectivity to bisphenol for the hydroxyalkylation of phenols to give bisphenol. Temperature Programmed Desorption (TPD) of ammonia and activity results of various catalysts showed that an appropriate combination of both strong and weak acidic sites in the catalyst was highly desirable for high bisphenol selectivity. A 10% DTP/SiO 2 catalyst was found to be highly selective for the cleavage of TBDMS ether into the corresponding alcohol at room temperature giving a high TON of 9.5 9 10 5 even after the 4th recycle. DTP was also found to be a promising solid acid catalyst for the intramolecular rearrangement of BPE giving 2-BP.

Cs salt of tungstophosphoric acid-promoted zirconium titanium phosphate solid acid catalyst: An active catalyst for the synthesis of bisphenols

“…This is very much coherent with the low temperature acid concentration (1.45%) which is maximum for 60CsTPA-ZTP. Our observation is in agreement with the report published by Rode et al 34 Similar observations were noticed on the formation of BPF with selectivity enhancement from 6.25-87.95% and With further increase in the wt% of CsTPA onto ZTP, the selectivity and rate of formation remain almost same. In case of BPA, biproducts such as chromans and triphenols were not identified, rather a minor quantity of o,p -BPA was observed at higher wt% of CsTPA (>50 wt%) supported ZTP.…”

“…As observed, the pristine ZTP 17 having highest surface area, i.e., 102 m 2 /g shows the lowest phenol conversion, i.e., 3% and 6.5%, lowest selectivity, i.e., 5% and 6.25% towards the formation of BPA and BPF, respectively. This is because of the fact that ZTP contains strong acidic sites at high temperature (HT), 33,34 which are not effective for the formation of p,p -BPA. Also, CsTPA shows the conversion, i.e., 10% towards BPA and BPF with 5% selectivity for BPA and 7.2% BPF.…”

“…In case of BPF formation, carbinol was identified as the side product since the trimer formation is favoured at HT acidic concentration. 34 The activity of 60 CsTPA-ZTP was studied towards the formation of BPA and BPF as a function of reaction time (figure 6). The experiments were carried out in the time range of 1-10 h. One can see, the conversion of phenol and selectivity towards the formation of p,p -BPA and BPF are rapidly increasing.…”

Montmorillonite-based heterogeneous catalysts for efficient organic reactions

“…The exchangeable cations between the mont layers can be readily replaced under mild conditions in various precursor solutions. For example, proton-exchanged mont (H-mont) is easily ion-exchanged by heating and stirring Na-mont at 90 °C in HCl aqueous solution (figure 2) [17]. For Al-mont, representative conditions are at 50 °C in AlCl 3 aqueous solution.…”

Biofuels additives derived via clay supported heteropoly acid catalyzed etherification of glycerol with t-butanol-biomass to liquid oxygenates

“…The glycerol etherification with isobutene using sulfonic acid functionalized solid acid showed the highest conversion of glycerol with high selectivity to di-and tri-glycerol ethers (79-91%) in comparison to non-sulfonated solid acid catalysts, which suggested that high activity and selectivity for etherification of glycerol can be achieved over catalysts with high acid strength and appropriate pore structure (Gonzalez et al 2013;Wilson and Clark, 2000;Garade et al 2010a). Hence, solid acids such as heteropoly acids (HPAs) supported catalysts could be a suitable option for etherification of glycerol due to higher Bronsted acid, recyclability, and stability (Sepulveda et al 2011;Rode et al 2009;Garade et al 2010a;Roze et al 2013;Liu et al 2013b;Magar et al 2017). The present studies have enhanced the economy of biodiesel production via conversion of by-product glycerol into oxygenated fuel additives.…”