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Catalyst synthesis is an art where an inefficient material can be remarkably converted into a highly active and selective catalyst by adopting a suitable synthetic strategy to tune its properties during synthesis. The underlying principle of the strategy presented here is the integration of tailoring the structural and chemical behavior of tin phosphates with tuned catalytic active centers directed by employing different structure directing agents (SDAs) and the attempt to understand this in detail. It is demonstrated how soft templates can be effectively used for their so far unknown utilization of tuning the active sites in phosphate containing catalysts. We found that, by using an appropriate synthesis strategy, it is possible to tune and control explicitly both the catalyst morphology and the nature of active sites at the same time. The 31P MAS NMR study revealed that employing SDAs in the synthesis strongly influenced the nature and amount of phosphate species in addition to porosity. The resultant different nanostructured SnPO catalysts were investigated for one-pot synthesis of alkyl levulinates via alcoholysis of furfuryl alcohol. Among the catalysts, SnPO-P123 exhibited greater butyl levulinate yield via alcoholysis of furfuryl alcohol with n-butanol and the study was extended to synthesize different alkyl levulinates. Importantly, the active sites in the SnPO-P123 catalyst responsible for the reaction were elucidated by a study using 2,6-lutidine as a basic probe molecule. This study therefore provides an avenue for rational design and construction of highly efficient and robust nanostructured SnPO catalysts to produce alkyl levulinates selectively.

We report a sulfonated hydrophobic mesoporous organic polymer (MOP-SO3H) as a highly efficient heterogeneous catalyst for one-pot 5-ethoxymethylfurfural (EMF) production from fructose in ethanol solvent. MOP-SO3H was fabricated by co-polymerization of divinylbenzene (DVB) and sodium p-styrene sulfonate (SPSS) followed by ion exchange with dilute H2SO4, and its pore structure and acid density could be tuned easily by varying the mole ratio of SPSS to DVB. 31P MAS NMR analysis using trimethylphosphine oxide as a base probe molecule indicated that MOP-SO3H possessed a weaker Bronsted acid site than conventional cation-exchange resins. The superhydrophobic properties of MOP-SO3H were retained even after incorporating a greater number of sulfonic acid groups into the polymer framework, while conventional solid acid resins exhibited hydrophilic properties. MOP-SO3H exhibited a superior catalytic performance in comparison with conventional acid resins, a mesoporous acid catalyst, and homogeneous acid catalysts in EMF production from fructose. After optimization of various reaction conditions using MOP-SO3H, a high EMF yield of 72.2% at 99.3% fructose conversion was achieved at 100 °C in a very short reaction time of 5 h. Notably, MOP-SO3H showed a much higher EMF formation rate than the Amberlyst-15 catalyst (53.5 vs. 6.1 μmol g−1 min−1). This superior performance of the MOP-SO3H catalyst was attributed to its unique feature of large surface area containing a large quantity of readily accessible acid sites distributed throughout the hydrophobic polymer framework. In addition to its high catalytic activity, the notable stability of the MOP-SO3H catalyst was also confirmed by leaching and recyclability tests. Thus, owing to its excellent catalytic performance and easy scalability, MOP-SO3H can potentially be used as an industrial heterogeneous catalyst to produce EMF from various fructose-containing biomass.

The generation of Brønsted (Sn–OH) and Lewis (coordinatively unsaturated metal centers) acidic sites on the solid surface is a prime demand for catalytic applications. Mesoporous materials are widely employed as catalysts and supports owing to their different nature of acidic sites. Nevertheless, the procedure adopted to generate acid functionalities in these materials involves tedious steps. Herein, we report the tunable acidic sites containing Brønsted sites with relatively varied acid strength in tin oxide by employing soft template followed by simple thermal treatment at various temperatures. The readily accessible active sites, specifically Brønsted acidic sites distributed throughout the tin oxide framework as well as mesoporosity endow them to perform with exceptionally high efficiency for epoxide ring opening reactions with excellent reusability. These features promoted them to surpass stannosilicate catalysts for the epoxide ring opening reactions with alcohol as a nucleophile and the study was extended to aminolysis of epoxide with the amine. The existence of relatively greater acid strength and numbers in T-SnO2-350 catalyst boosts to produce a high amount of desired products over other tin oxide catalysts. The active sites responsible in mesoporous tin oxide for epoxide alcoholysis were studied by poisoning the Brønsted acidic sites in the catalyst using 2,6-lutidine as a probe molecule.

Tin oxide is a versatile metal oxide because of its two characteristics; variable valence state and existence of oxygen vacancy defects. Therefore, tin oxide has potentially wide application in catalysis, electrocatalysis, solar energy conversion, antistatic coatings, transparent conductive electrodes, and electrochromic devices. Tin oxide-based materials play an important role in catalysis due to the existence of inherent acidic and redox characters. The properties in tin oxide can be modified by introducing cation or anion species in its structure and interaction with other oxides. This chapter focuses on the types of tin oxide-based materials viz., mesoporous and nano tin oxides, mixed metal oxide (M-Sn-oxide), composite metal oxide and tin oxide as catalyst support, and their applications in catalysis. They are reported as highly efficient catalysts in wide variety of reactions such as biomass conversion, biodiesel synthesis, glycerol transformations, Prins reaction, and cyclization reaction. Also, tin oxide-based materials are further discussed about their applications as catalysts in photocatalysis and photoelectrocatalysis for dye degradation and hydrogen evolution reactions.

Mesoporous tin oxide was prepared by template assisted and template-free methods. As-prepared materials were calcined at various temperatures to generate different nature (Bronsted and Lewis), amount and strength of acidic sites. The physico-chemical properties of the catalysts were studied by XRD, N2 sorption, pyridine-FTIR, NH3-TPD, DRS UV-vis, TGA, SEM, TEM, 1H MAS and 119Sn MAS NMR analyses. The catalytic behavior of mesoporous tin oxide catalysts was evaluated for acetalization and ketalization of glycerol with benzaldehyde and acetone respectively under solvent free conditions. The catalytic performance of mesoporous tin oxide was compared with that of other conventional solid acid catalysts namely H-ZSM-5, H-mordenite, H-beta, Al-MCM-41, Al-SBA-15 and Al-TUD-1. The efficiency of mesoporous tin oxide was also tested for cyclohexene epoxidation reaction. The catalyst prepared by template assisted method showed excellent catalytic performance compared to other catalysts due the difference in nature and amount of acidic sites in the catalyst. Meso-SnO2-T-350 was stable and reusable catalyst for four cycles without any appreciable loss in activity, and therefore it offers a good catalyst for potentially wide applications.

A sulfonic acid-functionalized mesoporous polymer (MP-SO3H) catalyst was prepared via post-synthetic modification of mesoporous polydivinylbenzene by incorporating a sulfonic acid moiety using conc. H2SO4. The synthesized materials were characterized via several physicochemical techniques and their performance was evaluated for the room-temperature liquid-phase acetalization of glycerol with acetone. The MP-SO3H catalyst performed better than other conventional solid acid catalysts, with a 94% glycerol conversion and 98.5% selectivity for solketal. The high activity of the MP-SO3H catalyst was attributed to the facile diffusion of reactants and products in the mesoporous environment as well as to the high acidity. Glycerol conversion increased with increase in the total acidity of the catalyst. In addition, the acidity and surface density of (H+) ions were found to have a direct correlation with the catalyst performance.

A bio-derived furfuryl alcohol transformation into various high-value chemicals is a growing field of interest among researchers. This study reports an exclusive investigation of the porosity and active sites responsible for the efficient alcoholysis of furfuryl alcohol to alkyl levulinate by the aid of zeolite catalyst. Alkyl levulinate is a promising platform chemical potentially used as a fuel additive and also for the production of chemicals. A detailed study using well-characterized HZSM-5 catalyst on the influence of acidity and post synthesis modification like desilication, dealumination, metal ion exchange and phosphate modification revealed the most desired type of acid sites required to catalyze this reaction. Among the HZSM-5 catalysts tested, HZSM-5 (SAR 95) showed the best performance of ≥ 99 % furfuryl alcohol conversion and 85 % butyl levulinate selectivity under optimum conditions. The catalyst exhibited good recyclability additionally addressing all the challenges reported in the previous literature fulfilling the green chemistry principles.

Metal hydroxy stannate is explored for the first time as a solid base catalyst for transesterification reactions. The catalyst was synthesized by co-precipitation method and characterized by PXRD, SEM, EDS, TGA, surface area and FT-IR measurements. In this work, we demonstrated metal hydroxy stannate as an efficient catalyst for the synthesis of biodiesel and to convert its byproduct glycerol into acetins. Performance of the catalyst was checked with both edible oil (sunflower) and non edible oils like waste cooking oil, jatropha, honge and simarouba. CaSn(OH) 6 gave high biodiesel yield with the tested oils at lower reaction temperature (65 °C). The performance of CaSn(OH) 6 was better than other solid base catalysts like CaO, MgO, Mg/Al HTc and KF/CaO. Separation of biodiesel from un-reacted oil and glycerol was carried out using solvent extraction method and isolated yield of biodiesel was calculated. Conditions like temperature, amount of catalyst and mole ratio were studied for both the reactions to get optimum yield of end products. Fuel properties of synthesized biodiesel were tested and compared with international standards. Catalyst showed good thermal stability and reusability with consistent activity for both the reactions.

The efficiency of mesoporous tin oxide as an acid catalyst in the activation of a carbonyl group through selected organic transformations involving the conversion of biomass derived molecules to value-added chemicals is reported. The mesoporous tin oxide was synthesized under ambient temperature using CTAB and was characterized by XRD, FT-IR, SEM, TEM, TGA, N2 sorption, TPD-NH3 and py-FT-IR. It was calcined at different temperatures, showing different physico-chemical properties, and exhibited a wormhole like topology with a large surface area of 160 m2 g−1. The py-FT-IR acidity measurement of the mesoporous tin oxide showed the presence of Bronsted and Lewis acid sites. These acid sites were sufficient to activate the carbonyl group of an aldehyde, a ketone, an acetic anhydride and an amide in selected important organic transformations such as Prins condensation, glycerol carbonylation with urea, ketalization of glycerol with cyclohexanone and acetylation of glycerol with acetic anhydride. In all the above catalytic processes, the mesoporous tin oxide showed superior performance compared to nano and bulk tin oxides. The mesoporous tin oxide catalyst also showed excellent recyclability and remarkable activity compared to the reported catalysts in all the reactions under study.

Mesoporous polymers (MP) were synthesized by free radical polymerization of divinylbenzene by a solvothermal method followed by sulfonic acid functionalization by a post synthetic modification with conc. H2SO4. MP-SO3H was characterized by various physicochemical techniques such as FT-IR, nitrogen sorption, CHNS analysis, acid–base titration and TGA. MP-SO3H was demonstrated to be a highly active heterogeneous acid catalyst, providing a high yielding route for the synthesis of h-GTBE through the etherification of bio-renewable glycerol with tert-butanol. MP-SO3H containing optimum acidity and a large mesoporous surface area gave 44% h-GTBE selectivity at 86% glycerol conversion under optimized reaction conditions. The catalytic performance of MP-SO3H was found to be superior over other conventional porous solid acid catalysts.

Octahedral MnO2 molecular sieve (OMS) was prepared using a hydrothermal synthesis route in the absence and the presence of urea. OMS was also prepared by a solvent-free method. Catalysts were characterized by the complementary combination of X-ray diffraction, N2 adsorption, scanning electron microscopy, UV–visible spectroscopy, thermogravimetric analysis, and NH3 and CO2 temperature-programmed desorption techniques. Catalysts were investigated in the oxidation of benzyl alcohols, hydration of aromatic/heterocyclic nitrile, and condensation reactions (Knoevenagel and Aldol). Furthermore, applicability of the catalyst was extended in one-pot tandem conversion of benzyl alcohol to 2-benzylidene-malononitrile, (E)-chalcone, and 2,3-dihydro-1,5-benzothiazepine. 2-Benzylidene-malononitrile and (E)-chalcone were prepared by a two-step tandem reaction from benzyl alcohol, whereas 2,3-dihydro-1,5-benzothiazepine was prepared by a three-step tandem reaction from benzyl alcohol. Recycling study showed that no signi...

Room temperature synthesis of solketal from acetalization of glycerol with acetone was carried out over various types of Bronsted solid acid catalysts in the liquid phase. Among the catalysts screened, H-Beta zeolite showed the best performance in less time period with 86% glycerol conversion and 98.5% selectivity to solketal. The chemical and structural properties of modified and unmodified beta catalysts were studied by X-ray diffraction, AAS, SEM, NH3-TPD and FTIR-pyridine adsorption. The H-Beta catalyst with lower crystallite size gave better conversion and solketal selectivity compared to H-Beta with higher crystallite size. The effect of acidity of the catalyst on acetalization of glycerol was studied by modified beta catalysts of varying acidities. Glycerol conversion decreased with decrease in total acidity of beta catalysts. Strong to weak acidity ratio of the catalysts was found to have a direct correlation with catalyst performance.

Glycerol acetylation and esterification reactions with acetic anhydride and acetic acid respectively give acetins, in which di and tri acetins are commercially important products used as fuel additives. Acetylation and esterification of glycerol were studied over various solid acid catalysts namely, cesium phosphotungstate, amberlyst-15, H-beta, sulfated zirconia and montmorillonite K-10 under mild reaction conditions. The catalysts were characterized by XRD, FTIR, SEM and acidity measurements. Among all the catalysts evaluated in this study, cesium phosphotungstate showed highest activity with >98% conversion for both the reactions, whereas di and triacetins selectivity was 99.1% for acetylation and 75% for esterification reaction. The catalyst with high Bronsted acidity gave high activity for both the reactions, whereas selectivity for di and tri acetins depends on nature of active sites.