This review covers the sustainable development of advanced improvements in CO2 capture and utilization.

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Ceria−praseodymia (CP) nanocrystalline solid solutions were prepared by a coprecipitation method and calcined at various temperatures to understand the thermal effects on the physicochemical properties of the nano-oxides. The structural and redox properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM-HREM), BET surface area (S BET), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), UV−visible diffuse reflectance spectroscopy (UV−vis DRS), and temperature programmed reduction (TPR) techniques. The catalytic efficiency toward oxygen storage capacity (OSC) and CO oxidation activity have been investigated. The XRD results confirmed the successful incorporation of praseodymium into the ceria lattice through the formation of nanoscale face-centered cubic solid solutions. The TEM-HREM observations supported the nanocrystalline nature of the solid solutions, as indicated by XRD results. XPS results revealed the presence of cerium and praseodymium in both 3+ and 4+ oxidation states, and surface enrichment of Pr. The UV−vis DRS results revealed an increase of Ce3+ species, indicating enhanced reducibility of the ceria upon Pr doping. Raman spectral analysis provided strong evidence for enhanced formation of oxygen vacancies inline with UV−vis DRS results. TPR measurements showed an enhanced bulk reduction at much lower temperatures, indicating increased oxygen mobility in the samples which enable the enhanced oxygen diffusion at lower temperatures. Ceria−praseodymia solid solutions were found to be thermally quite stable, and exhibit high oxygen storage capacity and CO oxidation activity even after calcination at high temperatures.

The utilization of CO 2 as a soft oxidant and promoter is a promising concept for industrial applications that could not only contribute to the mitigation of CO 2 levels, but also the development of economical and energy efficient syntheses of various chemicals. The abundant availability, non-toxic, economic and mild oxidizing properties of CO 2 has resulted in immense interest in its use as an oxidant in several reactions, such as the oxidative coupling of CH 4 and the oxidative dehydrogenation of alkanes and alkyl aromatics. At present, only a few processes based on CO 2 as a soft oxidant have been realised on a technical scale in spite of dedicated research. This review is intended to trace the emergence, application and understanding of such systems and shed light on the further development that may lead to industrial scale operations in the near future.

A systematic study was conducted to understand the influence of two different dopant cations (Zr4+ and Hf4+) incorporated into the ceria lattice. A modified coprecipitation technique was employed to make the investigated Ce x Zr1-x O2 (CZ) and Ce x Hf1-x O2 (CH) mixed oxides. The study was comprised of extensive characterization of the prepared catalysts using different techniques, namely, X-ray powder diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), transmission electron microscopy (TEM), UV−vis diffuse reflectance spectroscopy (UV−vis DRS), and BET surface area method. To assess the usefulness of these catalysts, oxygen storage−release capacity (OSC) and CO oxidation activity measurements were performed. The XRD analyses reveal that the CZ sample bears Ce0.75Zr0.25O2 and Ce0.6Zr0.4O2 phases and the CH sample possesses only the Ce0.8Hf0.2O2 phase after calcination at different temperatures (773−1073 K). RS measurements suggest a defective structure of the mixed oxides resulting in the formation of oxygen vacancies. The TEM results indicate nanometer-sized crystallites and there is no appreciable increase in the particle size even after high temperature treatments. The XPS studies reveal the presence of cerium in both Ce3+ and Ce4+ oxidation states. The ISS results indicate surface enrichment of cerium in the case of the CH sample, while such surface enrichment of cerium is not observed for the CZ sample. The UV−vis DRS measurements provide information about Ce4+ ← O2− and Ce3+ ← O2− charge transfer transitions. The absence of free ZrO2 and HfO2 in the mixed oxides tenders the clue about the formation of respective solid solutions. The CH catalyst exhibited better OSC and CO oxidation activity compared to that of the CZ sample. The OSC and CO oxidation activity results correlate well with the structural characterization data. The influence of ionic radii of dopant cations on the overall performance of the ceria-based mixed oxides is contemplated.

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