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•Key factors for dry reforming of methane (DRM).•Comprehensive review on role of catalytic properties for DRM.•Rational and suitable design of catalysts for DRM.•Interaction, size, ...basicity, oxygen storage capacity, reducibility and porosity.
Because the whole world is under threat from climate change, 195 countries decided to reduce greenhouse gas (GHG) emissions by adopting the “Paris Agreement”. The mitigation and utilization of GHG have become the most significant challenges in the area of green energy research. One feasible solution is the reforming of methane with carbon dioxide (called dry reforming of methane, DRM) that converts the two main GHGs (CO2 and CH4) into synthesis gas (H2 and CO), which is a resource for the manufacture of useful value-added products. The main issue that needs to be addressed for DRM is the deactivation of catalysts by sintering and carbon formation. Design of a viable catalyst that exhibits high catalytic activity and stability, as well as resistance against deactivation, could be accomplished by making appropriate choices of active metal, support, promoter, structure and methods for preparation and activation. Numerous studies and reviews have dealt with various aspects of DRM. This review focuses on the physicochemical properties of the pertinent catalysts and their role in the catalytic performance needed for DRM. Specifically, the interaction between components, dispersion, particle size, basicity, oxygen storage capacity, reducibility, porosity and surface area are discussed. This study provides the understanding of catalytic properties and their correlation with catalytic performance needed for the rational design of catalysts and suitable for DRM.
Effective adsorption of Congo red from an aqueous solution was achieved with a mesoporous Mg-Al mixed metal oxide (MMO). Both MMO-E and MMO-W were obtained via calcination of layered double ...hydroxides based on a P123 template in ethanol and water, respectively, resulting in different aggregation states. The effect of P123 phases on the morphology of MMO-E and MMO-W was investigated by X-ray diffraction, N2 adsorption-desorption isotherm, and scanning and transmission electron microscopies. MMO-E exhibited a sand-rose morphology whereas MMO-W carried small particles with relatively uniform interparticle pores. MMO-W accounted for remarkably large adsorption of Congo red up to 3470 mg/g, which was higher than 100% fractional occupancy. Adsorption kinetics of Congo red on MMO-E and MMO-W conformed to the pseudo-second-order kinetics, suggesting strong interactions between Congo red and both mixed metal oxides. Adsorption isotherms were described by the Langmuir model for MMO-E and Freundlich model for MMO-W, indicating effective multilayer adsorption of Congo red on MMO-W compared with monolayer adsorption on MMO-E. The uniform interparticle mesopores of MMO-W obtained by homogenous P123 micelles facilitated the adsorption of Congo red via intermolecular aggregation in the pore.
Remarkable Congo red adsorption of 3470 mg/g was achieved by forming uniform interparticle pores in a mixed metal oxide. The uniform pore was obtained utilizing Pluronic P123 as template. Layered metal hydroxide was developed along with homogeneous micelles of P123 in water, and calcined to obtain porous mixed metal oxide. Uniform interparticle pore in the oxide contributed to the favorable adsorption of Congo red through multilayer manner. Display omitted
•Homogeneous LDH-P123 composite was obtained in water medium.•MMO with homogeneous pore was obtained with P123 template.•MMO had uniform interparticle pores contributed to favorable adsorption of CR.•High CR adsorption on MMO up to 3470 mg/g was realized.•Multilayer adsorption with aggregates was a reason for the effective adsorption.
PurposeThis study seeks: (1) to identify whether the form of governance adopted (relational or contractual) drives suppliers' and buyers' collaboration in the same way; (2) to examine if both parties ...hold a similar view on the simultaneous use of both governance forms; and (3) to explore whether their perceptions on governance, collaboration and performance differ.Design/methodology/approachThe study used data from a survey of 150 matched buyer–supplier dyads from South Korea, using structural equation modeling (SEM) for the analysis.Findings(1) While governance mechanisms assist collaboration and affect operational and innovation outcomes, the significance and relative strength of the proposed relationships are perceived differently by buyers and suppliers. (2) Contrasting results are found regarding the interaction effect of the governance mechanisms on collaboration: a complementary relationship for the buyer and a substitutive relationship for the supplier.Originality/valueStudies on buyer–supplier relationships have yielded inconsistent results regarding whether the interactions of governance mechanisms function as substitutes or complements, because research has largely been conducted from the buyer's perspective, rather than the supplier's; this imbalanced view calls for integrated perspectives.
The use of calcium oxide (CaO) demonstrates a superior potential for the activation of ground granulated blast furnace slag (GGBFS), and it produces a higher mechanical strength than calcium ...hydroxide Ca(OH)2. The mechanical strength differences between CaO- and Ca(OH)2-activated GGBFS binders are explored using isothermal calorimetry, powder X-ray diffraction, thermogravimetric and differential thermal analysis (TGA and DTA) as well as compressive strength testing. Calcium silicate hydrate (C–S–H), Ca(OH)2 and a hydrotalcite-like phase are found as reaction products in all samples. The TGA and DTA results indicate that the use of CaO produces more C–S–H, although this is not likely to be the primary cause of higher strength development in the CaO-activated GGBFS. Rather, other factors such as porosity may govern the strength at a higher order of magnitude. Significant reduction of Ca(OH)2 occurs only with the use of Ca(OH)2, followed by the formation of carbonate (CaCO3), indicating carbonation.
•CaO showed a better potential for the activation of GGBFS than Ca(OH)2.•Strength test, XRD, TGA/DTA and isothermal calorimetry are used.•C-S-H, Ca(OH)2, and a hydrotalcite-like phase are found in all samples.•The use of Ca(OH)2 causes some degree of carbonation.
•Selected variables have a significant influence on yields of synthesis gas.•(CO2+H2O)/CH4 affects the temperature which can achieve the maximum conversion.•Coke is formed at low temperatures even ...with excess oxidizing agent.•The occurrence of RWGS becomes critical in real chemical reactions.•Equilibrium conversions are maintained for 500h without detectable deactivation.
Thermodynamic equilibrium analysis of the combined steam and carbon dioxide reforming of methane (CSCRM) and side reactions was performed using total Gibbs free energy minimization. The effects of (CO2+H2O)/CH4 ratio (0.9–2.9), CO2:H2O ratio (3:1–1:3), and temperature (500–1000°C) on the equilibrium conversions, yields, coke yield, and H2/CO ratio were investigated. A (CO2+H2O)/CH4 ratio greater than 1.2, a CO2:H2O ratio of 1:2.1, and a temperature of at least 850°C are preferable reaction conditions for the synthesis gas preparation in the gas to liquid process. Simulated conditions were applied to the CSCRM reaction and the experimental data were compared with the thermodynamic equilibrium results. The thermodynamic equilibrium results were mostly consistent with the experimental data, but the reverse water gas shift reaction rapidly occurred in the real chemical reaction and under excess oxidizing agent conditions. In addition, a long-term stability test (under simulated conditions) showed that the equilibrium conversion was maintained for 500h and that the coke formation on the used catalyst was not observed.
A
bstract
We explore conformally coupled scalar theory in AdS
6
extensively and their classical solutions by employing power expansion order by order in its self-interaction coupling λ. We describe ...how we get the classical solutions by diagrammatic ways which show general rules constructing the classical solutions. We study holographic correlation functions of scalar operator deformations to a certain 5-dimensional conformal field theory where the operators share the same scaling dimension ∆ = 3, from the classical solutions. We do not assume any specific form of the micro Lagrangian density of the 5-dimensional conformal field theory. For our solutions, we choose a scheme where we remove co-linear divergences of momenta along the AdS boundary directions which frequently appear in the classical solutions. This shows clearly that the holographic correlation functions are free from the co-linear divergences. It turns out that this theory provides correct conformal 2- and 3- point functions of the ∆ = 3 scalar operators as expected in previous literature. It makes sense since 2- and 3- point functions are determined by global conformal symmetry not being dependent on the details of the conformal theory. We also get 4-point function from this holographic model. In fact, it turns out that the 4-point correlation function is not conformal because it does not satisfy the special conformal Ward identity although it does dilation Ward identity and respect SO(5) rotation symmetry. However, in the co-linear limit that all the external momenta are in a same direction, the 4-point function is conformal which means that it satisfy the special conformal Ward identity. We inspect holographic
n
-point functions of this theory which can be obtained by employing a certain Feynman-like rule. This rule is a construction of
n
-point function by connecting
l
-point functions each other where
l < n
. In the co-linear limit, these
n
-point functions reproduce the conformal
n
-point functions of ∆ = 3 scalar operators in
d
= 5 Euclidean space addressed in arXiv:2001.05379.
The 2D transition metal carbides/nitrides (2D MXenes) are a versatile class of 2D materials for photovoltaic (PV) systems. The numerous advantages of MXenes, including their excellent metallic ...conductivity, high optical transmittance, solution processability, tunable work‐function, and hydrophilicity, make them suitable for deployment in PV technology. This comprehensive review focuses on the synthesis methodologies and properties of MXenes and MXene‐based materials for PV systems. Titanium carbide MXene (Ti3C2Tx), a well‐known member of the MXene family, has been studied in many PV applications. Herein, the effectiveness of Ti3C2Tx as an additive in different types of PV cells, and the synergetic impact of Ti3C2Tx as an interfacial material on the photovoltaic performance of PV cells, are systematically examined. Subsequently, the utilization of Ti3C2Tx as a transparent conductive electrode, and its influence on the stability of the PV cells, are discussed. This review also considers problems that emerged from previous studies, and provides guidelines for the further exploration of Ti3C2Tx and other members of the 2D MXene family in PV technology. This timely study is expected to provide comprehensive understanding of the current status of MXenes, and to set the direction for the future development in 2D material design and processing for PVs.
Recent progress on MXene‐based PVs is discussed. Synthesis procedures and properties of MXene are presented. The role of MXene as an additive, interfacial layer, and as a conductive electrode in PVs is comprehensively studied. Later, the influence of MXene on the stability of PVs is described. Finally, guidelines to overcome the challenges of MXene based materials for PVs are provided.
Although the different age groups had differences in sensitivity of asthma exacerbations (AEs) to environmental factors, no comprehensive study has examined the age-stratified effects of ...environmental factors on AEs.
We sought to examine the short-term effects in age-stratified groups (infants, preschool children, school-aged children, adults, and the elderly) of outdoor environmental factors (air pollutants, weather conditions, aeroallergens, and respiratory viral epidemics) on AEs.
We performed an age-stratified analysis of the short-term effects of 4 groups of outdoor environmental factors on AEs in Seoul Metropolitan City (Korea) from 2008 and 2012. The statistical analysis used a Poisson generalized linear regression model, with a distributed lag nonlinear model for identification of lagged and nonlinear effects and convergent cross-mapping for identification of causal associations.
Analysis of the total population (n = 10,233,519) indicated there were 28,824 AE events requiring admission to an emergency department during the study period. Diurnal temperature range had significant effects in pediatric (infants, preschool children, and school-aged children) and elderly (relative risk RR, 1.056-1.078 and 1.016, respectively) subjects. Tree and weed pollen, human rhinovirus, and influenza virus had significant effects in school-aged children (RR, 1.014, 1.040, 1.042, and 1.038, respectively). Tree pollen and influenza virus had significant effects in adults (RR, 1.026 and 1.044, respectively). Outdoor air pollutants (particulate matter of ≤10 μm in diameter, nitrogen dioxide, ozone, carbon monoxide, and sulfur dioxide) had significant short-term effects in all age groups (except for carbon monoxide and sulfur dioxide in infants).
These findings provide a need for the development of tailored strategies to prevent AE events in different age groups.
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Airborne pollens are one of the common causative and triggering agents of respiratory allergy in a changing planetary environment. A growing number of people worldwide are contracting allergic ...diseases caused by pollens. The seasonal variations in pollens have occurred everywhere and the sensitization rate to pollens has increased in children as well as in adults. Moreover, allergenic plants, such as ragweed and Japanese hop, grow in soil damaged by human's activities and deforestation with air pollution. It is impossible to avoid plants that cause allergies, because pollens can travel many kilometers in the breeze or wind. Hence, it is essential to survey and forecast pollens for the management of pollen allergy. Weather conditions may alter pollen concentrations. A number of studies have shown that increases in CO
concentration and atmospheric temperature raise pollen concentration. Hence most of the studies on the impact of climate change on aeroallergens must include the amount and allergenicity of pollens. It is yet unknown whether complex interactions with pollens, meteorological variables, and air pollutants in the changing environment. Considering the effect of climate change on the long-term trends in pollen levels and emerging viral infection, it is crucial to forecast and eliminate the associated risk for human health in future and take appropriate measures to reduce it.
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