Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.

Catalytic Properties of Ceria and CeO2-Containing Materials

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Advanced oxidation processes (AOP) for water purification and recovery

Since the time of the industrial revolution, the atmospheric CO(2) concentration has risen by nearly 35 % to its current level of 383 ppm. The increased carbon dioxide concentration in the atmosphere has been suggested to be a leading contributor to global climate change. To slow the increase, reductions in anthropogenic CO(2) emissions are necessary. Large emission point sources, such as fossil-fuel-based power generation facilities, are the first targets for these reductions. A benchmark, mature technology for the separation of dilute CO(2) from gas streams is via absorption with aqueous amines. However, the use of solid adsorbents is now being widely considered as an alternative, potentially less-energy-intensive separation technology. This Review describes the CO(2) adsorption behavior of several different classes of solid carbon dioxide adsorbents, including zeolites, activated carbons, calcium oxides, hydrotalcites, organic-inorganic hybrids, and metal-organic frameworks. These adsorbents are evaluated in terms of their equilibrium CO(2) capacities as well as other important parameters such as adsorption-desorption kinetics, operating windows, stability, and regenerability. The scope of currently available CO(2) adsorbents and their critical properties that will ultimately affect their incorporation into large-scale separation processes is presented.

Adsorbent Materials for Carbon Dioxide Capture from Large Anthropogenic Point Sources

Carbon capture and storage (CCS) is broadly recognised as having the potential to play a key role in meeting climate change targets, delivering low carbon heat and power, decarbonising industry and, more recently, its ability to facilitate the net removal of CO2 from the atmosphere. However, despite this broad consensus and its technical maturity, CCS has not yet been deployed on a scale commensurate with the ambitions articulated a decade ago. Thus, in this paper we review the current state-of-the-art of CO2 capture, transport, utilisation and storage from a multi-scale perspective, moving from the global to molecular scales. In light of the COP21 commitments to limit warming to less than 2 °C, we extend the remit of this study to include the key negative emissions technologies (NETs) of bioenergy with CCS (BECCS), and direct air capture (DAC). Cognisant of the non-technical barriers to deploying CCS, we reflect on recent experience from the UK's CCS commercialisation programme and consider the commercial and political barriers to the large-scale deployment of CCS. In all areas, we focus on identifying and clearly articulating the key research challenges that could usefully be addressed in the coming decade.

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Carbon capture and storage (CCS): the way forward

The flow pattern in a bubble column depends upon the column diameter, height, sparger design, superficial gas velocity and the nature of gas–liquid system. In this paper, the effect of some of these parameters have been simulated using Computational Fluid Dynamics (CFD). The relationship of these parameters with the interphase force terms has been discussed. A complete energy balance has been established. Using this methodology, the flow patterns reported by Hills (1974), Menzel et al. (1990), Yao et al. (1991) and Yu and Kim (1991) have been simulated. Excellent agreement has been shown between the CFD predictions and the experimental observations. The above model has been extended to homogenization of an inert tracer. In order to confirm this model, mixing experiments were carried out in a 200 mm i.d. bubble column. A radioactive tracer technique was used for the measurement of mixing time. Tc-99m (99mTc), in the form of sodium pertechnate salt, was used as the liquid phase tracer. Good agreement has been shown between the predicted and the experimental values of mixing time. The model was further extended for the estimation of axial dispersion coefficient (DL). Excellent agreement between the simulated and the experimental values of the axial dispersion coefficient confirms the predictive capability of the CFD simulations for the mixing process.



Le profil d'ecoulement dans une colonne a bulles depend du diameatre de la colonne, de sa hauteur, de la conception de l'aerateur, de la vitesse de gaz superficielle et de la nature du systeame gas—liquide. Dans cet article, l'effet de certains de ces parameatres a ete etudie par simulation numerique (CFD). La relation de ces parameatres avec les termes de force interphasique est discutee. Un bilan d'energie complet a ete etabli. A l'aide de cette methodologie, les profils d'ecoulement signales par Hills (1974), Menzel et al. (1990), Yao et al. (1991) et Yu et Kim (1991) ont ete simules. On a montre un excellent accord entre les predictions de la CFD et les observations experimentales. Le modeale ci-dessus a ete etendu a l'homogeneisation d'un traceur inerte. Afin de confirmer ce modeale, des experiences de melange ont ete menees dans une colonne a bulles de 200 mm de diameatre interieur. Une technique de traceur radioactif a ete utilisee pour la mesure du temps de melange. On a utilise 7e-99m (99m Te), sous forme de sel de pertechnate de sodium, comme traceur de la phase liquide. Un bon accord a ete trouve entre les valeurs predites et les valeurs experimentales du temps de melange. Le modeale a ensuite ete etendu pour l'estimation du coefficient de dispersion axiale (DL). Un excellent accord entre les valeurs simulees et les valeurs experimentales du coefficient de dispersion axiale confirme la capacite predictive des simulations de CFD pour le procede de melange.

CFD modeling of flow, macro‐mixing and axial dispersion in a bubble column

Direct numerical simulations of a freely falling sphere using fictitious domain method: Breaking of axisymmetric wake

Aone-dimensional model has been developed to predict liquid phase velocities in bubble columns. The closures of liquid phase material balance, gas phase material balance and energy balance are provided to give predictive capability to the model. A solution procedure has been developed to predict the hold-up profile and liquid phase velocity profile in the bubble columns. The model has been used to compare the experimental data over a wide range of column diameter and gas-liquid systems. An excellent agreement has been shown between predicted and experimental data of all the above cases. The model is extended to predict the velocity profiles in 0.15m diameter column for a range of superficial gas velocity of 0.06

Jyeshtharaj B. Joshi

Papers

CFD modeling of flow, macro‐mixing and axial dispersion in a bubble column

Direct numerical simulations of a freely falling sphere using fictitious domain method: Breaking of axisymmetric wake

A Comprehensive One-Dimensional Model for Prediction of Flow Pattern in Bubble Columns

Modeling and Simulation of a Spray Column for NOx Absorption

Lipozyme deactivation by butanol and temperature