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Bio-ethanol plant derived crude lignin was utilized in the synthesis of carbon catalysts for the conversion of xylose in acid pretreatment liquid (APL, another by-product of bio-ethanol plant) into furfural. Also, xylose dehydration to furfural by carbon catalysts carried out in water-MIBK biphasic system showed a maximum yield of 60% furfural. In addition, a carbon catalyst modified with 1 N H2SO4 was found to be highly active as concentrated acids reported earlier in the open literature. Only a small part of the total crude lignin from the bio-ethanol plant was utilized in this manner. Further research is necessary on the valorization of remaining crude lignin waste.

Au-Pd alloy nanoparticles supported on basic anion-exchange resin (AER) have exceptional catalytic activity for the oxidation of 5-hydroxymethyl-2-furfural (HMF) into 2,5-furan dicarboxylic acid (FDCA) with an equimolar amount of base. SEM-EDX and TEM analyses show that 5–20 nm Au-Pd alloy nanoparticles are well dispersed both on the resin surface and inside resin spheres by a simple procedure without any assistance of additives. XPS analysis reveals that Au- and Pd metals exist in an alloy form on the AER support, which is confirmed by a comparison study with a mixture of AER-supported monometallic nanoparticles (AER-supported Au and AER-supported Pd). In the presence of a 1:1 ratio of Au-Pd alloy nanoparticles over Amberlite IRA-743 resin with O 2 (10 bar) at 373 K in an equimolar Na 2 CO 3 aqueous solution, HMF is oxidized to FDCA with a 93.2% yield. On the other hand, mixture of AER-supported Au and AER-supported Pd affords only a 52% FDCA yield under identical conditions. This catalyst can be used 6 times without any significant loss of activity. FDCA is also obtained from HMF with an 82.9% yield in air (40 bar).

Polyethylene terephthalate (PET) is the third-largest globally produced polymer, and many efforts have been made to replace PET with a renewable polymer. One renewable alternative to PET is polyethylene furanoate (PEF), which is prepared using 2,5-furan dicarboxylic acid (FDCA) as a precursor instead of terephthalic acid (TPA). Biomass-derived hydroxymethyl-2-furfural (HMF) can be converted to 2,5-furan dicarboxylic acid (FDCA) through multiple oxidation reactions. Metal oxide-supported Ru catalyst prepared by simple methods for the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furan dicarboxylic acid (FDCA) in the absence of a base under aqueous conditions is reported. This study clearly explains that the nature of basicity of the support has an important role on the selective oxidation of HMF to FDCA. Among the various materials studied magnesium oxide (MgO)-supported Ru catalyst afforded a 100% HMF conversion and more than 90% FDCA yield with 90 psi of $$\hbox {O}_{2}$$ at 160 $${^{\circ }}\hbox {C}$$ in 4 h and it could be used 5 times without a significant drop of FDCA yields. Metal oxide-supported Ru catalyst prepared by simple methods for the oxidation of 5-Hydroxymethylfurfural (HMF) to 2,5-Furan dicarboxylic acid (FDCA) in the absence of a base under aqueous conditions are reported. Magnesium oxide (MgO)-supported Ru catalyst afforded a 100% HMF conversion and more than 90% FDCA yield.

Heterogeneous selective oxidation of 5-hydroxymethyl-2-furfural (HMF) into 2,5-diformylfuran (DFF) using molecular oxygen and vanadium catalyst onto activated carbon in MIBK, extracting solvent for HMF, is described. Highly stable V2O5 supported on activated carbon catalyst was synthesized using V3 + (VCl3) precursor and confirmed by XPS analysis, which found to be highly active. A maximum HMF conversion of > 95% with > 96% DFF selectivity was achieved and this heterogeneous catalyst could be used 4 times without any significant loss of activity.

Petroleum-independent and economically viable production of 5-hydroxymethyl-2-furfural (HMF) from industrially supplied high fructose corn syrup (HFCS) using a wood powder-derived carbonaceous solid acid in an ethylene glycol (EG)-based solvent was developed. EG-based solvents were preferable to the dehydration of HFCS into HMF owing to stabilizing reversible intermediates. In addition, low boiling EG-based solvents were readily removed to isolate HMF. As a parametric study on the dehydration of HFCS into HMF in an EG-based solvent, effects of reaction temperature, initial concentration of fructose, catalyst dosage, and water content on reaction rate and HMF yield were investigated. Sulfonated amorphous carbonaceous materials (∼0.7 mmol of SO3H/g) were prepared from wood powder via incomplete hydrothermal carbonization and then sulfonization, and they were applied to the dehydration of HFCS in glyme, affording HMF in 80% yield. It was also found that a prolonged reaction enabled further conversion of HMF ...

Onsite remediation of phosphate in wastewaters remains a challenge in water treatment technologies. Further, aftermath of the treated material is hitherto unknown and mostly disposed of as land-fill. A new method for onsite remediation of phosphate is proposed using colloidal layered double hydroxide (LDH) nanosheets and the treated material is valorized as phosphate release fertilizer. Nitrate containing NiAl-LDHs was prepared by hexamine hydrolysis and the colloidal suspension of LDH nanosheets was obtained by dispersing the wet cake in water through three different methods namely ultrasonication, mechanical shaking and hydrothermal. These nanosheets were explored for phosphate remediation; the quantity of phosphate removed depended on the amount of LDH present in the colloidal suspension. Powder X-ray diffraction, TEM, and UV–vis diffuse reflectance spectroscopic measurements revealed that the uptake is due to restacking of nanosheets. The uptake of phosphate was rapid for UD-LDH compared to parent powdered LDH; however, settling of nanosheets was hindered at higher than the stoichiometric amount of UD-LDH and is reasoned through zeta potential measurements. Uptake of phosphate was similar in wide pH range (4.5–11) while decreased sharply at lower pH. Selective uptake of phosphate in enriched seawater and sustained removal of phosphate in simulated “model pond systems” were achieved for UD-LDH. The restacked material after phosphate removal was utilized as an effective phosphate release fertilizer for the growth of a common green seaweed Ulva lactuca . Tapping the potential of colloidal LDH nanosheets for wastewater remediation and ingeniously using the treated material, here as fertilizer, offers a new approach with dual benefits.

5-Hydroxymethyl-2-furfural (HMF) was prepared with high fructose corn syrup (HFCS) manufactured directly from industry. Equipped industrial process and cheaper availability considered HFCS-90 as a competitive starter for production of HMF. Readily evaporable solvent, 1,4-dioxane was found as a promising reaction media from the screening of various solvents and readily available cation exchange resin, Amberlyst-15 was used as a solid acid catalyst. Parametric variation studies including amount of catalyst, concentration of HFCS-90, and reaction temperature were performed to achieve a maximum HMF yield of 80% at 100 °C within 3 h. In particular, use of readily evaporable solvent and heterogeneous catalyst allowed highly practical purification of HMF, which still remains as a major obstacle to the commercialization of HMF. With filtration, evaporation, and extraction, HMF was simply isolated in 72% yield and 1H NMR spectra of the isolated HMF confirmed that its purity was sufficient for use in next step of reactions. In addition, all solvents could be recycled with distillation and catalyst was reused up to 5 cycles without a significant loss of activity.

Selective oxidation of 5-hydroxymethyl-2-furfural (HMF) to 2,5-diformylfuran (DFF) toward industrial production was studied over Ru supported γ-alumina catalyst using molecular oxygen as an oxidant. From the solvents screening, considering recyclability after reaction, toluene was found to be the best solvent and gave maximum conversion of 99% with 97% DFF selectivity at 130 °C and 40 psi O2 pressure. Catalyst was washed with NaOH solution of pH = 12 to remove the adsorbed polymer impurities and then reused up to 5 cycles. The product could be purified by simple evaporation of the solvent, which could add advantage for industrial process.

Phenol, an important bulk organic compound, has diverse applications encompassing both industry and society. Commercially, it is produced through energy intensive three-step cumene process operating at relatively low yield with the co-production of acetone. Several attempts were made for producing phenol through challenging one-step direct hydroxylation of benzene using different oxidants like O2, N2O and H2O2. Liquid phase hydroxylation of benzene using H2O2 found to be more attractive due to its low reaction temperature and environmentally friendly nature (as water is only formed as by-product). The hydroxylation reaction occurs through Fenton’s mechanism; however along with phenol several other products are also formed due to higher reactivity of phenol compared to benzene. Our research group has been working on this reaction for nearly a decade using layered double hydroxides (LDHs) and their derived forms as heterogeneous selective oxidation catalyst. Screening of different LDHs having different metal ions in the layers revealed the necessity of copper for hydroxylation in pyridine. Addition of co-bivalent metal ion along with copper was made in an endeavour to improve the activity that revealed the promising results for CuZnAl LDHs. Efforts were then made to shift from pyridine to environmentally benign solvent, water, for this reaction that showed reasonably good yields with very high selectivity of phenol. Addition of small amount of sulfolane as a co-solvent increased the selectivity for phenol further. The reusability difficulty faced while using as-synthesized LDHs was overcome when calcined LDHs were used. Structure–property-activity relationships were deduced to understand the results observed. The present review besides covering our work also provides the state-of-art on this reaction using different oxidants with emphasis on H2O2.

Selective hydroxylation of benzene to phenol using H 2 O 2 as the oxidant was studied over copper-containing layered double hydroxides (LDHs) and their calcined oxides containing different co-bivalent ions (Mg, Zn, Ni or Co). In all the catalysts studied, the Cu/M(II) ratio was 10/90, the trivalent metal ion was aluminum and an atomic ratio of the bivalent to the trivalent metal ion was about 3.0. Catalysts were synthesized using co-precipitation under conditions of low supersaturation and were characterized by various physicochemical methods. Samples with zinc as the co-bivalent ion showed high activity whereas cobalt showed the least activity in both the as-synthesized and calcined forms. The high catalytic activity of the zinc-containing compound was attributed to the facile formation of Cu + , the likely active species for this reaction, as confirmed through X-ray photoelectron spectroscopy (XPS) measurements. Solvent variation studies revealed that water was the best solvent and that addition of a small amount of sulfolane as the co-solvent increased the selectivity for phenol. The calcined CuZnAl oxide catalyst can be reused up to three cycles without any significant change in the yield of phenol. The retention of the dispersion of copper verified through energy dispersive X-ray analysis (EDAX) measurements was likely to be responsible for the recyclability.

Solid–solid inter-polytype transformations are observed during the thermal dehydration of sulfate-containing layered double hydroxides (LDHs). The metal hydroxide layer behaves as a “structural synthon” and the interconversion of polytypes of rhombohedral and hexagonal symmetries takes place by rigid translations of successive layers by (± 1/3, ± 2/3) relative to one another in the ab plane. These translations are selected among the many possible, as they preserve the coincidence of the symmetry elements of the individual layers and thereby conserve the threefold symmetry of the crystal across the inter-polytype conversions. As a result, these transformations are enthalpically not expensive. These translations are facilitated at near ambient temperatures (30–60 °C) by the reversible dehydration of the LDH, which involves the deinsertion/insertion of water molecules within the restricted space of the interlayer region.

The layered double hydroxide (LDH) of Co with Al decomposes to yield an oxide residue with the spinel structure below 250°C. The decomposition reaction is preceded by the formation of an intermediate hydroxide in which the metal hydroxide layers are regularly stacked about the c-crystallographic axis, but the layers themselves are aperiodic. Aperiodicity is modeled by locating randomly chosen Co2+ ions in tetrahedral sites in the interlayer region. This phase is characterized by a single strong basal reflection in its powder diffraction pattern. All other reflections are extinguished on account of (i) turbostratic disorder which destroys all hkl reflections and (ii) layer aperiodicity, which destroys all two dimensional hk reflections. Given its topochemical relationship with the spinel structure, such an intermediate is a necessary precursor to spinel formation.

Copper containing layered double hydroxides (LDHs) with less than 1 atom % Cu along with different cobivalent ions such as magnesium, zinc, nickel or cobalt at (Cu+M(II))/Al atomic ratio 3.0 were synthesized. Calcination of these materials offered mixed metal oxides (refereed here as CLDHs) without any discrete copper oxide phase as confirmed by PXRD and STEM analysis. Hydroxylation of phenol to catechol (CAT) and hydroquinone (HQ) was carried out over both as-synthesized and calcined materials. Among the cobivalent ions, zinc containing samples both in the as-synthesized and calcined forms showed very high activity while cobalt showed the minimum. Variation of copper content for CuZnAl ternary system (0.009 atom % to 0.056 atom %) showed a maximum activity for the sample with 0.038 atom % (CuZnAl-5-CLDH). High activity was attributed to better dispersion of isolated copper species as inferred through TPR measurements. Highly active CuZnAl-5-CLDH can be reused up to three cycles without any significant ch...

Isomerisation of allylbenzene to β-methyl styrene ( cis + trans ) has been successfully carried out over Mg and Ni containing as-synthesized hydrotalcites (HTs). The samples screened by varying the M(II)/Al atomic ratio showed that MgAl4–HT and NiAl4–HT (M(II)/M(III) atomic ratio is around 4.0) exhibited a maximum conversion of 99% and 95% respectively at 160 °C using DMF as solvent in 6 h. Studies were done to discern the surface basicity of these samples through CO 2 temperature programmed desorption and phenol adsorption. Both measurements gave reasonable correlation with isomerisation activity. This reaction can be studied as a model reaction for assessing basicity of as-synthesized HTs augmenting the earlier results of Aramendia et al. for calcined HTs (Aramendia, 2002, 2004).

Catalysts with the hydrotalcite-like structure and general formula NiCuAlyz-HT having (Ni + Cu)/Al atomic ratio of 3.0 with varying Ni:Cu atomic compositions (100:0–50:50) were synthesized, characterized and tested for isomerization of eugenol to isoeugenol. The decrease in the activity upon addition of copper to NiAl lattice is investigated through temperature programmed reduction and phenol adsorption. Conversion of eugenol over active NiAl hydrotalcite significantly decreased upon incorporation of Cu2+ in the NiAl binary lattice wherein substitution of 25 at% of Ni2+ by Cu2+ annihilated the isomerization activity. The decrease in the activity upon addition of copper to NiAl lattice is investigated through physiochemical studies.

Multicomponent one-pot synthesis of Hantzsch dihyropyridine (DHP) was achieved by the condensation of benzaldehyde, ethyl acetoacetate and ammonium acetate at room temperature using environmentally friendly as-synthesised medicinally acceptable hydrotalcites (HT) and hydrotalcite-like (HT-like) materials as solid base catalysts. The multifunctional activity of these materials is again proved by this important reaction. Among the catalysts screened, MgAl2-HT (Mg/Al atomic ratio = 2.0) showed maximum yield (61% in 6.5 h using acetonitrile as solvent). We propose that the high activity of this catalyst may be attributed to cooperative contribution of acid–base bifunctional sites. The versatility of these materials was checked by employing various aldehydes (acyclic, cyclic and aromatic) which showed reasonable yields of DHPs over MgAl2-HT. To our knowledge, this is the first report wherein HT and HT-like materials performed as catalysts for this multicomponent reaction and also the first case of employing a solid base catalyst for DHP synthesis.

The use of fragrance chemicals is known to have begun thousands of years ago. During the early years, the fragrant chemicals were used only in perfumery notes. This scenario was changed in the 20th century by the modernization in lifestyle. Today, the fragrant chemicals are dovetailed into our daily lives not only in perfumery, but also in food, beverages, cosmetics, soaps, detergents, and household items, etc. The global market for fragrance chemicals, including perfumes, in 2012 was around US$ 23 billion and forecast to be US$ 33 billion by 2015. The sources of these chemicals are largely plant-based. Traditionally, they are extracted from plants and are used as such, but sometime require conversion to other chemical substances (synthetic) to produce different aromas. In recent years, most are synthesized in laboratories given the lack of the right kind of plant material. The chemical transformations involved in these reactions and some of them practiced in the industries (which are largely closely guarded) involve catalysis that encompasses homogeneous, heterogeneous, and bio-catalysis. Most of the homogeneous catalytic routes often encounter environmentally unfriendly materials, such as corrosive alkali or acids, or soluble forms of toxic metals that generate large waste which are often disposed of improperly, causing a concern to the environment, while bio-catalytic routes are very specific and expensive. New methods/approaches are being developed using heterogeneous catalysts for the synthesis of perfumery molecules, with an eye on atom economy and E-factor as prime movers, thanks to their inherent advantages, including cost competitiveness. In this chapter, we cover a broad industrial outlook on fragrance chemicals, including the intellectual property scenario, approaches made through homogeneous and bio-catalytic routes, and address in detail heterogeneous catalytic methods for the synthesis of diverse perfumery molecules, through different classes of reactions, including our own contribution that comprises isomerization. We conclude by giving opportunities and future directions in the field of perfumery chemicals, where heterogeneous catalysis is ordained to play an important role in the years to come.

A simple, environmentally benign green synthesis of silver nanoparticles was achieved using lemon fruit extract (Citrus lemon). The synthesized silver nanoparticles were characterized using UV-Vis spectroscopy, infrared spectroscopy, powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM). The predominantly spherical mono dispersed 2 to 10 nm sized silver nanoparticles were obtained for the first time using lemon extract. The anti-microbial activity of silver nanoparticles was also explored. Lemon extract-mediated synthesis is cost efficient, eco-friendly and an easy alternative to conventional methods of silver nanoparticles synthesis.

One-step synthesis of carbonate-free nitrate containing LDHs was achieved using hexamine hydrolysis at low temperature and the products were delaminated successfully in water; materials showed total delamination in formamide while restacking behavior depended critically on the medium.

Cubic microparticles of Co3O4 spinel were synthesized by calcination of CoCO3 obtained using CoAl layered double hydroxide (LDH) as a unitary precursor through soft-chemical decomposition. The obtained cobalt spinel showed an exceptionally high electrical conductivity at room temperature. This is attributed to high concentrations of charge carriers (Co4+), unique morphology, high reduction temperature and low activation barrier. This journal is © the Partner Organisations 2014. Refereed/Peer-reviewed

Fatty acid methyl esters (FAME) were produced from edible, non-edible and used cooking oils with different fatty acid contents by transesterification with methanol using calcined layered double hydroxides (LDHs) as solid base catalysts. Among the catalysts, calcined CaAl2-LDH (hydrocalumite) showed the highest activity with90% yield of FAME using low methanol:oil molar ratio (6:1) at 65 °C in 5 h. The activity of the catalyst was attributed to its high basicity as supported by Hammett studies and CO(2)-TPD measurements. The catalyst was successfully reused in up to four cycles. Some of the properties such as density, viscosity, neutralization number and glycerol content of the obtained biodiesel matched well with the standard DIN values. It is concluded that a scalable heterogeneously catalyzed process for production of biodiesel in high yields from a wide variety of triglyceride oils including used oils is possible using optimized conditions.