Lakshmi Katta

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 characteristics and catalytic performance of alumina-supported nanosized ceria–lanthana solid solutions

Alumina-supported nanosized ceria–lanthana solid solutions (CeO2−La2O3/Al2O3 (CLA) = 80 : 20 : 100 mol% based on oxides) were synthesized by a modified deposition coprecipitation method from ultra-high dilute aqueous solutions. The synthesized materials were subjected to various calcination temperatures from 773 to 1073 K to understand the surface structure and the thermal stability. Structural and redox properties were deeply investigated by different characterization techniques, namely, X-ray diffraction (XRD), Raman spectroscopy (RS), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (H2-TPR), and Brunauer–Emmett–Teller (BET) surface area. The catalytic efficiency was evaluated for CO oxidation at normal atmospheric pressure. BET surface area measurements revealed that synthesized samples exhibit reasonably high specific surface area. As revealed by XRD measurements, samples maintain structural integrity up to 1073 K without any disproportionation of phases. XPS results suggested that there is no significant change in the Ce3+ amount during thermal treatments due to the absence of undesirable cerium aluminate formation. A significant number of oxygen vacancies were confirmed from Raman and UV-vis DRS measurements. The CLA 773 sample exhibited superior CO oxidation activity. The better activity of the catalyst was proved to be due to a high dispersion in the form of nanosized ceria–lanthana solid solutions over the alumina support, facile reduction, and a high oxygen storage capacity.

Nanosized Unsupported and Alumina-Supported Ceria-Zirconia and Ceria-Terbia Solid Solutions for CO Oxidation

Ceria-zirconia (CZ) and ceria-terbia (CT) and alumina-supported ceria-zirconia (CZA) and ceria-terbia (CTA) solid solutions were synthesized by coprecipitation and deposition precipitation methods, respectively. Structural characteristics and catalytic activity of the synthesized samples have been investigated using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), and Brunauer-Emmett-Teller (BET) surface area measurements. To evaluate the catalytic properties, total oxygen storage capacity and CO oxidation activity measurements were carried out. The XRD analyses revealed the formation of Ce0.75Zr0.25O2 phase for CZ and Ce0.5Zr0.5O2 and Ce0.6Zr0.4O2 phases for CZA samples, respectively. While the formation of only Ce0.8Tb0.2O2-δ phase was noted for both CT and CTA samples. All the supported and unsupported samples adopted a fluorite-type structure and exhibited cell parameters with respect to Vegards rule. The HRTEM results indicated well-dispersed particles of the size around 5 nm. The RS measurements suggested the presence of oxygen vacancies due to defective structure formation. The XPS studies revealed the presence of cerium in both Ce4+ and Ce3+ oxidation states in different proportions. It was found that CO oxidation for CTA occurs at very much lower temperature than CT, CZ, and CZA samples. Details of these findings by correlating with the structural characterization studies are consolidated.

The effect of ceria on the dynamics of CuO-Cu2O redox transformation: CuO-Cu2O hysteresis on ceria

CuO supported on ceria and alumina is prepared by incipient wetness impregnation and its redox behavior is investigated by means of XRD, XPS and TPO experiments. CuO on ZrO2 and on ceria–zirconia are also synthesized for comparison. The support plays a major role on the dynamics of CuO–Cu2O transformation. On Al2O3 the formation of CuAl2O4 inhibits any oxygen exchange during TPO experiments, while on ceria, zirconia and ceria–zirconia supported catalysts CuO decomposition and re-oxidation take place with a hysteresis similar to that observed for Pd–PdO transformation. On CeO2 the hysteresis is significantly reduced, indicating a strong effect of ceria on CuO–Cu2O redox cycle.Graphical Abstract

Interfacial interaction driven CO oxidation: nanostructured Ce1−xLaxO2−δ/TiO2 solid solutions

Titania supported ceria–lanthana solid solutions (CexLa1−xO2−δ/TiO2; CLT) have been synthesized by a facile and economical route. Existence of synergism between ceria–lanthana (CL) solid solutions and titania-anatase phase, which leads to decrease in the crystallite size, retarded titania phase transformation, and improved redox properties, has been thoroughly investigated by various techniques, namely, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (UV–vis DRS), Raman spectroscopy (UV–RS and Vis–RS), BET surface area analysis, and temperature programmed reduction (TPR). Two key observations made from the whole exercise were (i) mutual interaction of Ce and Ti ions could impose typical Ce–O–Ti modes at the interfacial region and (ii) the La3+ ion as a dopant provokes a large number of oxygen vacancies via a charge compensation mechanism. The promising role of these factors in the CO oxidation (one of the most formidable challenges) has been comprehensively described. The observed enhanced activity for the CLT sample is primarily attributed to an apparent specific orientation of the active component over the support, which is endorsed by the interfacial interaction. This specific mode could facilitate the CO adsorption with simultaneous bulk oxygen diffusion for more consumption and in turn better activity.