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.

/pdf/carbon-capture-and-storage-ccs-the-way-forward-11rgsqyer0.pdf

Carbon capture and storage (CCS): the way forward

Axial mixing in laminar pipe flows

The knowledge of the flow patterns of each phase of bubble column reactors is of considerable importance for the rational design and scale-up The hydrodynamic models for the liquid phase have been reviewed The models have been based on some form of pressure balance or energy balance These two approaches have been compared and recommendations have been made regarding the range of applicability of the individual models A comparison between the predicted and the experimental liquid velocities has been presented whenever possible The range of variables has been pointed out for which further investigations are needed The empirical and theoretical models for the mixing behavior of the different phases of bubble column reactors have also been reviewed

Invited review hydrodynamic and mixing models for bubble column reactors

A comparison of thermal-hydraulic performance of various fin patterns using 3D CFD simulations

Solid-fluid heat-transfer coefficients have an important role in the design of chemical processing equipment. The major resistance to heat transfer lies in a region very close to the wall, where experimental measurements are very difficult. The validity and accuracy of the models developed for the estimation of the heat- and mass-transfer coefficient still do not have general applicability for the entire range of Reynolds and Prandtl numbers, because of the limited knowledge of near-wall turbulence. There have been two approaches for such model development: one is an analytical approach, which considers the momentum, mass, and heat transfer to be analogous in nature and the understanding of one of these processes can be used to predict the other two; the other approach is heuristic, based on the visualization of the behavior of the coherent structures in the near-wall region. The continuous movement of fluid elements to and away from the wall (coherent structures) affects the transport phenomena. The models for the quantification of this behavior have been developed for the estimation of heat- and mass-transfer rates in the literature. However, both these approaches contain parameters fitted empirically to obtain good agreement with the experimental heat- and mass-transfer data. These models must be tested for their formulation and empirical constants on the basis of accurate solutions of governing equations of heat, mass, and momentum transfer. This is possible using direct numerical simulation (DNS) and large eddy simulation (LES), which can accurately predict the near-wall flow pattern. An attempt has been made to exploit the ability of DNS and LES to develop insight into hitherto used models, based on analogies and/or heuristic arguments.

Insight into Theories of Heat and Mass Transfer at the Solid-Fluid Interface Using Direct Numerical Simulation and Large Eddy Simulation

Design and scale-up of fluid catalytic cracking (FCC) riser is still largely empirical, owing to limited understanding of inherent multiphase flow in this equipment. The multiphase flow of FCC riser has therefore been extensively investigated both experimentally and computationally. The experiments have provided significant insight into gas–solid flow patterns inside cold-flow risers, but simultaneous observations on flow and performance parameters (conversion and yields) in FCC riser are rarely found in literature. Consequently, computational fluid dynamic (CFD) models of FCC riser that can simultaneously account for flow, interphase interactions, droplet vaporization and cracking kinetics have been developed. The CFD modelling of FCC riser, despite several efforts, has still remained a challenge as it requires careful consideration of governing equations and closure models. This review presents state-of-the-art in CFD modelling and experimental analysis of gas–solid hydrodynamics and reactive flow of FCC riser. The CFD models are explained in greater detail with governing equations, constitutive relations, and physical significance of all the terms. A brief review of DNS studies on cluster formation, gas–solid drag, and turbulent interactions is also presented. Impact of important closure models such as drag models, viscous stress models, boundary conditions, droplet vaporization models, and kinetic models on predictions is critically examined. The review identifies major shortcomings of current CFD models and makes detailed recommendations for future work.

Jyeshtharaj B. Joshi

Papers

Axial mixing in laminar pipe flows

Invited review hydrodynamic and mixing models for bubble column reactors

A comparison of thermal-hydraulic performance of various fin patterns using 3D CFD simulations

Insight into Theories of Heat and Mass Transfer at the Solid-Fluid Interface Using Direct Numerical Simulation and Large Eddy Simulation

Computational fluid dynamic modelling of FCC riser: A review