Baithy Mallesham

Design of highly efficient Mo and W-promoted SnO2 solid acids for heterogeneous catalysis: acetalization of bio-glycerol

Development of highly promising solid acids is one of the key technologies to meet the essential challenges of economical and environmental concerns. Thus, novel molybdenum and tungsten promoted SnO2 solid acids (wet-impregnation) and pure SnO2 (fusion method) were prepared. The synthesized catalysts were systematically analyzed using various techniques, namely, XRD, BET surface area, pore size distribution, XPS, FTIR, FTIR of adsorbed pyridine, Raman, NH3-TPD, and H2-TPR. XRD results suggested formation of nanocrystalline SnO2 solid solutions due to the incorporation of molybdenum and tungsten cations into the SnO2 lattice. All the materials exhibited smaller crystallite size, remarkable porosity, and high specific surface area. Raman measurements suggested the formation of more oxygen vacancy defects in the doped catalysts, and the TPR results confirmed facile reduction of the doped SnO2. NH3-TPD studies revealed the beneficial role of molybdenum and tungsten oxides on the acidic properties of the SnO2. FTIR studies of adsorbed pyridine showed the existence of a larger number of Bronsted acidic sites compared to Lewis acidic sites in the prepared catalysts. The resulting catalysts are found to be efficient solid acids for acetalization of glycerol with acetone, furfural, and its derivatives under solvent-free and ambient temperature conditions. Particularly, the Mo6+-doped SnO2 catalyst exhibited excellent catalytic performance in terms of both glycerol conversion and selectivity of the products. The increased presence of acidic sites and enhanced specific surface area, accompanied by notable redox properties and superior lattice defects are found to be the decisive factors for better catalytic activity of the Mo6+-doped SnO2 sample. The investigated SnO2 solid acids represent a novel class of heterogeneous catalysts useful for the transformation of glycerol to value-added products in an eco-friendly manner.

Designing CuOx Nanoparticle-Decorated CeO2 Nanocubes for Catalytic Soot Oxidation: Role of the Nanointerface in the Catalytic Performance of Heterostructured Nanomaterials

This work investigates the structure-activity properties of CuOx-decorated CeO2 nanocubes with a meticulous scrutiny on the role of the CuOx/CeO2 nanointerface in the catalytic oxidation of diesel soot, a critical environmental problem all over the world. For this, a systematic characterization of the materials has been undertaken using transmission electron microscopy (TEM), transmission electron microscopy-energy-dispersive X-ray spectroscopy (TEM-EDS), high-angle annular dark-field-scanning transmission electron microscopy (HAADF-STEM), scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS), X-ray diffraction (XRD), Raman, N2 adsorption-desorption, and X-ray photoelectron spectroscopy (XPS) techniques. The TEM images show the formation of nanosized CeO2 cubes (∼25 nm) and CuOx nanoparticles (∼8.5 nm). The TEM-EDS elemental mapping images reveal the uniform decoration of CuOx nanoparticles on CeO2 nanocubes. The XPS and Raman studies show that the decoration of CuOx on CeO2 nanocubes leads to improved structural defects, such as higher concentrations of Ce(3+) ions and abundant oxygen vacancies. It was found that CuOx-decorated CeO2 nanocubes efficiently catalyze soot oxidation at a much lower temperature (T50 = 646 K, temperature at which 50% soot conversion is achieved) compared to that of pristine CeO2 nanocubes (T50 = 725 K) under tight contact conditions. Similarly, a huge 91 K difference in the T50 values of CuOx/CeO2 (T50 = 744 K) and pristine CeO2 (T50 = 835 K) was found in the loose-contact soot oxidation studies. The superior catalytic performance of CuOx-decorated CeO2 nanocubes is mainly attributed to the improved redox efficiency of CeO2 at the nanointerface sites of CuOx-CeO2, as evidenced by Ce M5,4 EELS analysis, supported by XRD, Raman, and XPS studies, a clear proof for the role of nanointerfaces in the performance of heterostructured nanocatalysts.

Physicochemical characterization and catalytic CO oxidation performance of nanocrystalline Ce–Fe mixed oxides

The development of an efficient doped CeO2 material is an active area of intense research in environmental catalysis. In this study, we prepared highly promising Ce–Fe nano-oxides by a facile coprecipitation method and their catalytic performance was studied for CO oxidation. Various characterization techniques, namely, XRD, BET surface area, pore size distribution, Raman, FT-IR, TEM, H2-TPR, and XPS were used to correlate the structure–activity properties of the Ce–Fe catalysts. XRD results confirmed the formation of nanocrystalline Ce1−xFexO2−δ solid solution due to doping of Fe3+ into the CeO2 lattice. The BET surface area and lattice strain of CeO2 are significantly improved after the Fe-incorporation. Raman studies revealed the presence of abundant oxygen vacancies in the Ce–Fe sample. TEM images evidenced the formation of nanosized particles with an average diameter of 5–20 nm in the prepared samples. Interestingly, despite the thermal treatment at higher temperatures, the Ce–Fe sample showed remarkable reducible nature compared to pure CeO2 ascribed to existence of strong interaction between the CeO2 and FeOx. The synthesized Ce–Fe nano-oxides calcined at 773 K exhibited excellent CO oxidation performance (T50 = 480 K), with a huge difference of 131 K with respect to pure CeO2 (T50 = 611 K). The outstanding activity of the Ce–Fe catalyst is mainly due to smaller crystallite size, facile reduction, enhanced lattice strain, and ample oxygen vacancies. The superior CO oxidation performance of Ce–Fe nano-oxides with the advantages of low cost and easy availability could make them potential alternatives to noble metal-based oxidation catalysts.

Highly efficient cerium dioxide nanocube-based catalysts for low temperature diesel soot oxidation: the cooperative effect of cerium- and cobalt-oxides

Co3O4 promoted CeO2 nanocubes have been found to exhibit outstanding catalytic activity for the oxidation of diesel soot at low temperatures (50% soot conversion = 606 K). This remarkable performance is attributed to the superior reducible nature of cerium oxide and the preferential exposure of CeO2 (100) and Co3O4 (110) facets. A probable mechanism based on the cooperative effect of cerium- and cobalt-oxides has been proposed, offering new possibilities for the design of promising materials for catalytic soot oxidation.

Preparation of silica supported ceria–lanthana solid solutions useful for synthesis of 4-methylpent-1-ene and dehydroacetic acid

The intriguing research toward the exploitation of ceria-based materials for various applications has been growing significantly. In the present investigation, we describe the preparation, characterization and utilization of CeO2–La2O3 (CL) and CeO2–La2O3/SiO2 (CLS) solid solutions for the synthesis of two industrially useful chemicals namely 4-methylpent-1-ene and dehydroacetic acid. Coprecipitation and deposition coprecipitation from ultrahigh dilute solutions were used for the synthesis of CL and CLS catalysts, respectively. The physicochemical characterization has been achieved with the help of various techniques namely X-ray diffraction (XRD), BET surface area, transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), Raman spectroscopy (UV-RS and Vis-RS), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) measurements. The structure–activity relationships helped to correlate different parameters that are necessary for obtaining desired products in good yields. The inclusion of silica support has an optimistic influence on the acid–base properties of the ceria–lanthana, in terms of both amount and strength of sites. The presence of silica not only manipulates the acid–base properties but also causes numerous benefits, for instance, it improves the dispersion, stabilizes the active component against sintering and enriches the oxygen vacancy concentration. The meticulous analysis of characterization and activity studies revealed the significant role of acid–base sites in directing the desired products. Interestingly, the CLS catalyst has shown better performance in the production of both 4-methylpent-1-ene and dehydroacetic acid compared to the unsupported CL sample due to well-balanced acid–base sites.

Eco-friendly synthesis of bio-additive fuels from renewable glycerol using nanocrystalline SnO2-based solid acids

The present work has been undertaken with an aim to synthesize valuable bio-additive fuels from glycerol acetalization using SnO2-based solid acids. Various promoters, namely SO42−, MoO3 and WO3 were incorporated to the SnO2 using a wet-impregnation method. An extensive physicochemical characterization has been achieved by means of XRD, BET surface area, BJH analysis, FT-IR, pyridine adsorbed FT-IR, NH3-TPD, ICP-OES and XPS techniques. The BET surface area of SnO2 is significantly improved from 11 to 32, 56 and 41 m2 g−1 after the addition of the WO3, MoO3, and SO42− promoters, respectively. The XPS studies revealed that Sn is present in the +4 oxidation state, whereas Mo, W and S are in the +6 oxidation state in the prepared samples. In addition, the SO42−/SnO2 sample contained super acidic sites, along with strong- and medium-acidic sites. The amount of acidic sites was found to be 46.47, 61.81, 81.45 and 186.98 μmol g−1 for the SnO2, WO3/SnO2, MoO3/SnO2, and SO42−/SnO2 samples, respectively. The pyridine adsorbed FT-IR studies revealed the existence of a superior quantity of Bronsted acidic sites than Lewis acidic sites in the synthesized catalysts. Promoted SnO2 catalysts exhibited a promising catalytic performance for glycerol acetalization with acetone and furfural, and the activity of the catalysts was found to increase in the following order: SnO2 < WO3/SnO2 < MoO3/SnO2 < SO42−/SnO2. The outstanding performance of the SO42−/SnO2 catalyst is mainly due to the existence of a large amount of acidic sites associated with the super acidic sites. The achieved optimum glycerol conversions with acetone and furfural were ~98 and 99% over the SO42−/SnO2 catalyst, respectively.

β-Cyclodextrin supported MoO3–CeO2 nanocomposite material as an efficient heterogeneous catalyst for degradation of phenol

With the aim of efficiently degrading organic pollutants through an easily operated procedure, a series of MoO3–CeO2 and β-cyclodextrin supported MoO3–CeO2 nano-composite materials were synthesized by using a co-precipitation method. A surfactant such as Cetyl Trimethyl Ammonium Bromide (CTAB) was used during the synthesis of this nano-composite material. These prepared catalysts are thoroughly characterized by various techniques such as XRD, BET, FT-IR, pyridine adsorbed FT-IR, Raman spectroscopy, SEM and TEM. The XRD study results suggested the formation of nanocrystalline materials which is also clearly observed from the SEM and TEM analysis. Raman measurements disclosed the presence of oxygen vacancies and lattice defects in all synthesized nano-composite samples. The catalytic activities of the synthesized materials were successfully tested for the degradation of phenol by using hydrogen peroxide at room temperature. It is surprising that the phenol degradation efficiency of the β-cyclodextrin supported MoO3–CeO2 nano-composite material is exhibited higher than that of other materials, which has been mainly attributed to the promoting effect of β-cyclodextrin. The degradation reaction is carried out at room temperature with continuous stirring and without light irradiation. Therefore, this degradation reaction is different from conventional heterogeneous catalysis or photocatalysis, in which the pollutants cannot be degraded completely, but it may transform from one phase to another phase. The gradual decrease in COD value shows the degradation of phenol that leads to the conversion of organic compounds into harmless gaseous CO2 and inorganic ions. Thus, this reported phenol degradation reaction is a quite promising green technology, which could be widely applied in practice.

Highly efficient continuous-flow oxidative coupling of amines using promising nanoscale CeO2–M/SiO2 (M = MoO3 and WO3) solid acid catalysts

The development of promising solid acid catalysts alternative to hazardous liquid acids is essential towards a sustainable chemical industry. This work reports the synthesis of nanostructured CeO2–MoO3/SiO2 and CeO2–WO3/SiO2 solid acids, along with CeO2–MoO3, CeO2–WO3 and CeO2 for continuous-flow oxidative coupling of benzylamine using O2 as a green oxidant. A systematic physicochemical characterization has been undertaken using XRD, Raman, N2 adsorption–desorption, TEM, NH3-TPD, and XPS techniques. It was found that the dispersion of CeO2–MoO3 and CeO2–WO3 species on the SiO2 support leads to remarkable structural and acidic properties, due to the synergetic effect of the respective components. TEM analysis reveals the presence of highly dispersed WO3 (0.8–1.2 nm) and MoO3 (0.8–1 nm) nanoparticles in the synthesized catalysts. Among the various catalysts developed, the CeO2–MoO3/SiO2 sample exhibited higher BET surface area (248 m2 g−1), abundant oxygen vacancy defects, and large amounts of strong acidic sites. Owing to improved properties, the CeO2–MoO3/SiO2 solid-acid showed a superior catalytic performance in the continuous-flow oxidative coupling of benzylamine: the obtained benzylamine conversions for 1 h are ∼11.8, 55, 70, 76, and 96%, respectively, for CeO2, CeO2–WO3, CeO2–WO3/SiO2, CeO2–MoO3, and CeO2–MoO3/SiO2 catalysts. Importantly, the CeO2–MoO3/SiO2 solid acid exhibited a remarkable steady performance in terms of benzylamine conversion (∼88–96%) and selectivity of N-benzylbenzaldimine product (∼96–97.8%) up to 6 h. The outstanding catalytic performance of CeO2–MoO3/SiO2 solid acid coupled with the application of continuous-flow synthesis, economical benefits of the respective oxides, and eco-friendly oxidant is expected to bring new opportunities in the design of industrially-favourable chemical processes.