Putla Sudarsanam

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.

Nanocrystalline Ce1−xSmxO2−δ (x = 0.4) solid solutions: structural characterization versus CO oxidation

A nanocrystalline Ce–Sm–oxide solid solution, with an excellent redox property and remarkable oxygen storage/release capacity, has been synthesized by means of a simple and highly practicable coprecipitation method. To understand the thermal and textural stability, the synthesized catalyst was subjected to calcination at various temperatures (773–1073 K). Physicochemical characterization was achieved using XRD, HRTEM, BET surface area, Raman, ICP-OES, XPS, TG-TDA, UV-vis DRS, TPR, and FTIR techniques, and the catalytic performance was evaluated for the oxidation of CO. Coprecipitation of Ce4+ and Sm3+ ions through ultra-high dilute solutions provided the single phase Ce0.6Sm0.4O2−δ solid solution in the nanoscale range, as confirmed by XRD and TEM studies. Raman studies revealed two types of lattice defects, namely, oxygen vacancies and MO8 complex defects due to disparity in the oxidation state and ionic radius of Sm3+ and Ce4+, respectively. Calculations made from XPS atomic ratios (Ce/Sm) and Raman band intensity ratios (AD1/AF2g) indicated migration of Sm from the bulk to the surface at elevated temperatures that caused a negative effect on the oxygen vacancy concentration. The doping of Sm3+ into the ceria lattice effectively enhanced the reduction behaviour of ceria by shifting the surface and bulk reduction to lower temperatures. Remarkably, Sm-incorporation showed an optimistic influence on the oxygen storage ability and CO oxidation efficiency of ceria attributed to profound lattice defects and enhanced bulk oxygen mobility. The salient features of physicochemical characterization versus catalytic CO oxidation efficiency of Ce–Sm–oxide solid solutions have been elaborated in this article.

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.

An efficient noble metal-free Ce–Sm/SiO2 nano-oxide catalyst for oxidation of benzylamines under ecofriendly conditions

A nanosized Ce–Sm/SiO2 catalyst was found to show an outstanding performance in the oxidation of benzylamines into valuable dibenzylimine products with almost 100% selectivity with O2 as the green oxidant under solvent-free conditions, which is attributed to the presence of abundant strong acidic sites, enhanced oxygen vacancy concentration, and superior BET surface area.

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.

Rare earth metal doped CeO2-based catalytic materials for diesel soot oxidation at lower temperatures

In this work, the influence of trivalent rare-earth dopants (Sm and La) on the structure-activity properties of CeO2 was thoroughly studied for diesel soot oxidation. For this, an optimized 40% of Sm and La was incorporated into the CeO2 using a facile coprecipitation method from ultra-high dilute aqueous solutions. A systematic physicochemical characterization was carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), Brumauer-Emmett-teller method (BET) surface area, X-ray photoelectron spectroscopy (XPS), Raman, and H2-temperature programmed reduction (TPR) techniques. The soot oxidation efficiency of the catalysts was investigated using a thermogravimetric method. The XRD results suggested the formation of nanocrystalline single phase CeO2-Sm2O3 and CeO2-La2O3 solid solutions. The Sm- and La-doped CeO2 materials exhibited smaller crystallite size and higher BET surface area compared with the pure CeO2. Owing to the difference in the oxidation states of the dopants (Sm3+ and La3+) and the Ce4+, a number of oxygen vacancies were generated in CeO2-Sm2O3 and CeO2-La2O3 samples. The H2-TPR studies evidenced the improved reducible nature of the CeO2-Sm2O3 and CeO2-La2O3 samples compared with the CeO2. It was found that the addition of Sm and La to the CeO2 outstandingly enhanced its catalytic efficiency for the oxidation of diesel soot. The observed 50% soot conversion temperatures for the CeO2-Sm2O3, CeO2-La2O3 and CeO2 were ∼790, 843 and 864 K (loose contact), respectively, and similar activity order was also found under the tight contact condition. The high soot oxidation efficacy of the CeO2-Sm2O3 sample was attributed to numerous catalytically favourable properties, like smaller crystallite size, larger surface area, abundant oxygen vacancies, and superior reducible nature.

Promising ceria–samaria-based nano-oxides for low temperature soot oxidation: a combined study of structure–activity properties

The design of promising heterogeneous catalysts is an urgent task for protecting the environment from automotive exhaust pollutants. In this work, the catalytic efficiency of nanosized Ce–Sm and Ce–Sm/γ-Al2O3 samples synthesized using economical coprecipitation and deposition coprecipitation methods, respectively, was investigated for diesel soot oxidation. The physicochemical properties of the synthesized materials were systematically analyzed by means of XRD, BET surface area, Raman spectroscopy, TG-DTA, FT-IR spectroscopy, HRTEM, ICP-OES, XPS, and UV-vis DRS techniques. XRD studies confirmed the formation of nanocrystalline single-phase Ce–Sm oxide solid solutions. HRTEM images showed the presence of small-sized nanocrystals (∼4–15 nm) in the synthesized samples. The Ce–Sm/γ-Al2O3 sample exhibited remarkable thermal stability compared with the Ce–Sm oxide and CeO2 samples, as evidenced by an insignificant variation in the crystallite size and BET surface area with high temperature thermal treatments. Owing to the disparity in the oxidation state of Sm3+ and Ce4+, abundant oxygen vacancies were formed in both the Ce–Sm and Ce–Sm/γ-Al2O3 samples. Interestingly, the oxygen vacancy concentration substantially decreased with increased calcination temperature, attributed to the high level of order of the samples. The catalytic activity results revealed that both the Ce–Sm and Ce–Sm/γ-Al2O3 samples show excellent soot oxidation performance compared with pristine CeO2 due to the presence of abundant oxygen vacancies and superior BET surface area. A 50% soot conversion was achieved at ∼690, 697 and 835 K with the Ce–Sm, Ce–Sm/γ-Al2O3 and CeO2 samples calcined at 773 K, respectively. It was found that the soot oxidation efficiency of the Ce–Sm and Ce–Sm/γ-Al2O3 samples strongly depends on the calcination temperature. Despite its trivial activity difference with respect to the Ce–Sm sample, the outstanding thermal stability of the Ce–Sm/γ-Al2O3 sample is vital in view of the practical working conditions of diesel engines.

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.

Structural evaluation and catalytic performance of nano-Au supported on nanocrystalline Ce0.9Fe0.1O2−δ solid solution for oxidation of carbon monoxide and benzylamine

In this work, we systematically investigated the structure–activity performance of nanosized Au/CeO2 and Au/Ce0.9Fe0.1O2−δ catalysts, along with nanocrystalline CeO2 and Ce0.9Fe0.1O2−δ supports, for the oxidation of carbon monoxide and benzylamine. An extensive physicochemical characterization was undertaken using XRD, BET surface area, BJH analysis, TG-DTA, XPS, TEM, Raman, AAS and CHN analyses. XRD studies confirmed the formation of smaller sized Ce0.9Fe0.1O2−δ nanocrystallites due to the incorporation of Fe3+ ions into the CeO2 lattice. Interestingly, Raman analysis revealed that the addition of Au remarkably improves the structural properties of the supports, evidenced by F2g peak shift and peak broadening, a significant observation in the present work. TEM images revealed the formation of smaller Au particles for Au/Ce0.9Fe0.1O2−δ (∼3.6 nm) compared with Au/CeO2 (∼5.3 nm), attributed to ample oxygen vacancies present on the Ce0.9Fe0.1O2−δ surface. XPS studies indicated that Au and Fe are present in metallic and +3 oxidation states, respectively, whereas Ce is present in both +4 and +3 oxidation states (confirming its redox nature). Activity results showed that the incorporation of Fe outstandingly enhances the efficacy of the Au/CeO2 catalyst for both CO oxidation and benzylamine oxidation. A 50% CO conversion was achieved at ∼349 and 330 K for Au/CeO2 and Au/Ce0.9Fe0.1O2−δ catalysts, respectively. As well, the Au/Ce0.9Fe0.1O2−δ catalyst showed ∼99% benzylamine conversion with ∼100% dibenzylimine selectivity for 7 h reaction time and 403 K temperature, whereas only 81% benzylamine conversion was achieved for the Au/CeO2 sample under similar conditions. The excellent performance of the Au/Ce0.9Fe0.1O2−δ catalyst is mainly due to the existence of smaller Au particles and an improved synergetic effect between the Au and the Ce0.9Fe0.1O2−δ support. It is confirmed that the oxidation efficiency of the Au catalysts is highly dependent on the preparation method.