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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.
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•Demand for H2 necessitated the development of a compact reformer.•Core unit process of compact reformer includes SRM, WGS, and PROX.•Scale-down of reformer decrease thermal ...efficiency and increase processing capacity.•This review introduces the studies about each core unit and provides a guide.•It especially focuses on the selection of appropriate materials in catalysts.
Climate change triggered by the excessive use of fossil fuels has resulted in an increased focus on the use of hydrogen. In addition to its clean property, hydrogen exhibits a higher efficiency for fuel cell applications compared to heat engines. Although hydrogen is one of the most common elements on Earth, it is not readily available in its elemental form in nature, indicating that it is a secondary energy source that requires the processing of hydrocarbons or water. Currently, hydrogen is predominantly produced using fossil fuels (96%), and the large-scale production of hydrogen from natural gas has already been commercialized. However, the increasing demand for on-site/distributed power generation systems has necessitated the development of a small-scale hydrogen production process. This scale-down induces a decrease in thermal efficiency and an increase in processing capacity, which compels the development of an integrated and harmonized technology. Studies are being conducted on compact reformers in this regard. The core unit processes of compact reformer include steam reforming of methane (SRM), water–gas shift (WGS), and preferential CO oxidation (PROX), with each process requiring the development of customized catalysts. This review introduces the basic thermodynamics and kinetics of these core unit processes, details their various issues, and provides a guide regarding current research trends on the development of customized catalysts for the unit processes of SRM, WGS, and PROX in compact reformers. State of the art for compact reformers are also introduced, showing that there are only several types of commercial compact reformers yet compared to their importance.
•Methane productivity of unacclimatized and acclimatized sludge were investigated.•Biogas produced in ASS showed higher methane content (65–76%) than in USS (26–73%).•The ASS exhibited greater ...degradation of LCFAs than in USS.•Firmicutes, Bacteroidetes, Synergistetes and Euryarchaeota were highly increased.•Abundance of Syntrophomonas and Methanosarcina in ASS improved methane generation.
The methane productivity and long chain fatty acids (LCFAs) degradation capability of unacclimatized seed sludge (USS) and acclimatized seed sludge (ASS) at different substrate ratios of fats oil and grease (FOG) and mixed sewage sludge were investigated in this study. Biogas produced in ASS in initial phase of anaerobic digestion had higher methane content (65–76%) than that in USS (26–73%). The degradation of major LCFAs in the ASS was 22–80%, 33–191%, and 7–64% higher for the substrate ratios of 100:10, 100:20, and 100:30, respectively, as compared to the LCFAs’ degradation in USS. Microbial acclimatization increased the population of Firmicutes (40%), Bacteroidetes (32%), Synergistetes (10%), and Euryarchaeota (8%) in ASS, which supported the faster rate of LCFAs degradation for its later conversion to methane. The significant abundance of Syntrophomonas and Methanosarcina genera in ASS supported faster generation rate of methane in an obligatory syntrophic relationship.
Urbanization, industrialization, and natural earth processes have potentially increased the contamination of heavy metals (HMs) in water bodies. These HMs can accumulate in human beings through the ...consumption of contaminated water and food chains. Various clean-up technologies have been applied to sequester HMs, especially conventional methods including electrolytic technologies, ion exchange, precipitation, chemical extraction, hydrolysis, polymer micro-encapsulation, and leaching. However, most of these approaches are expensive for large-scale projects and require tedious control and constant monitoring, along with low efficiency for effective HMs removal. Algae offer an alternative, sustainable, and environmentally friendly HMs remediation approach. This review presents a state-of-the-art technology for potential use of algae as a low-cost biosorbent for the removal of HMs from wastewater. The mechanisms of HMs removal, including biosorption and bioaccumulation along with physical and chemical characterization of the algae are highlighted. The influence of abiotic factors on HMs removal and changes in algal biocomponents (including, carbohydrate, lipid, and protein) are discussed. Recent progresses made in the development of HMs-tolerant algal strains and the direction of future research toward the development of sustainable technology for advanced wastewater treatment and biomass production are covered.
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•Toxicological effects of ciprofloxacin on C. mexicana was studied.•96h EC50 of ciprofloxacin for C. mexicana was 65mgL−1.•Ciprofloxacin influenced the biochemical characteristics of ...microalgal cells.•MDA and SOD of C. mexicana were significantly increased by ciprofloxacin.•Sodium acetate acts as an electron donor and enhanced ciprofloxacin removal.
This study evaluated the toxicity and cellular stresses of ciprofloxacin (CIP) and its co-metabolic removal in a freshwater microalga Chlamydomonas mexicana. The toxicological effects of CIP on C. mexicana were assessed by studying the growth and biochemical characteristics of the microalga including total chlorophyll, carotenoid content, malondialdehyde (MDA) and superoxide dismutase (SOD) activity. The calculated effective concentration (EC50) of CIP on C. mexicana was 65±4mgL−1 at 96h. The growth of C. mexicana was significantly inhibited at increased concentrations of CIP, showing 36±1, 75±3. and 88±3% inhibition at 40, 60 and 100mgL−1 CIP, respectively, compared to the control after 11days of cultivation. The total chlorophyll, carotenoid, MDA and SOD activity were significantly increased as a result of relatively high concentrations of CIP stress. C. mexicana showed 13±1% removal of CIP (2mgL−1) after 11days of cultivation; however, the addition of an electron donor (sodium acetate, 4gL−1) highly enhanced the removal of CIP (2mgL−1) by>3-fold after 11days. Kinetic studies showed that removal of CIP followed a first-order model (R2 0.94–0.97) with the apparent rate constants (k) ranging from 0.0121 to 0.079 d−1.
•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.
•Wastewater treatment with algal biomass production was evaluated in a bench-scale.•C. vulgaris and S. obliquus showed μopt values of 1.39 and 1.41day−1, respectively.•Complete removal (>99%) of TN ...and TP by both algal strains was observed.•Harvesting efficiency of M. oleifera was 81% for C. vulgaris and 92% for S. obliquus.
Microalgae, Chlorella vulgaris and Scenedesmus obliquus were cultivated in a small scale vertical flat-plate photobioreactor (PBR) supplemented with municipal wastewater in order to achieve simultaneous wastewater treatment and biomass production for biofuel generation. Microalgal growth and nutrient removal including total nitrogen (TN), total phosphorus (TP), total inorganic carbon (TIC) and trace elements (Ca2+, Na+, Mg2+ and Zn2+) were monitored during microalgae cultivation. C. vulgaris and S. obliquus showed optimal specific growth rates (μopt) of 1.39 and 1.41day−1, respectively, and the TN and TP were completely removed (>99%) from the wastewater within 8days. Microalgal biomass in the PBR was harvested using a natural flocculant produced from Moringa oleifera seeds. The harvesting efficiency of M. oleifera was 81% for C. vulgaris and 92% for S. obliquus. The amounts of saturated, mono-unsaturated, and poly-unsaturated fatty acids in the harvested biomass accounted for 18.66%, 71.61% and 9.75% for C. vulgaris and 28.67%, 57.14% and 11.15% for S. obliquus, respectively. The accumulated fatty acids were suitable to produce high quality biodiesel with characteristics equivalent to crop seeds oil-derived biodiesel. This study demonstrates the potential of microalgae-based biodiesel production through the coupling of advanced wastewater treatment with microalgae cultivation for low-cost biomass production in a PBR.
This study focuses on the applicability of single‐atom Mo‐doped graphitic carbon nitride (GCN) nanosheets which are specifically engineered with high surface area (exfoliated GCN), NH2 rich edges, ...and maximum utilization of isolated atomic Mo for propylene carbonate (PC) production through CO2 cycloaddition of propylene oxide (PO). Various operational parameters are optimized, for example, temperature (130 °C), pressure (20 bar), catalyst (Mo2GCN), and catalyst mass (0.1 g). Under optimal conditions, 2% Mo‐doped GCN (Mo2GCN) has the highest catalytic performance, especially the turnover frequency (TOF) obtained, 36.4 h−1 is higher than most reported studies. DFT simulations prove the catalytic performance of Mo2GCN significantly decreases the activation energy barrier for PO ring‐opening from 50–60 to 4.903 kcal mol−1. Coexistence of Lewis acid/base group improves the CO2 cycloaddition performance by the formation of coordination bond between electron‐deficient Mo atom with O atom of PO, while NH2 surface group disrupts the stability of CO2 bond by donating electrons into its low‐level empty orbital. Steady‐state process simulation of the industrial‐scale consumes 4.4 ton h−1 of CO2 with PC production of 10.2 ton h−1. Techno‐economic assessment profit from Mo2GCN is estimated to be 60.39 million USD year−1 at a catalyst loss rate of 0.01 wt% h−1.
This study removes atmospheric CO2 into epoxide through CO2 cycloaddition and concurrently produces value‐added products. Exfoliated g‐C3N4 nanosheets catalyst with highly exposed NH2 edges (electron‐donating) and isolated molybdenum atom (electron‐withdrawing) are engineered to reduce the activation energy barrier of CO2 and propylene oxide to enhance propylene carbonate formation. Techno‐economic assessment is estimated based on operating conditions and long‐term stability results.
A comprehensive ecotoxicological evaluation of a sulfamethazine (SMZ) and sulfamethoxazole (SMX) mixture was conducted using an indicator microalga, Scenedesmus obliquus. The toxicological effects of ...this mixture were studied using microalgal growth patterns, biochemical characteristics (total chlorophyll, carotenoid, carbohydrate, fatty acid methyl ester), and elemental and Fourier-transform infrared spectroscopy analyses. The 96-h half maximal effective concentration (EC50) of the SMZ and SMX mixture was calculated to be 0.15 mg L−1 according to the dose-response curves obtained. The chlorophyll content decreased with elevated SMZ and SMX concentrations, while the carotenoid content initially increased and then decreased as concentration raised. The unsaturated fatty acid methyl esters (FAMEs) content was enhanced with higher SMZ and SMX concentrations, while that of saturated FAMEs simultaneously decreased due to SMZ and SMX stress. Elemental analyses showed an improved percentage of nitrogen and sulfur in the microalgal biomass as SMZ and SMX concentrations increased. The microalga S. obliquus was shown to biodegrade the chemicals tested and removed 31.4–62.3% of the 0.025–0.25 mg SMZ L−1 and 27.7–46.8% of the 0.025–0.25 mg SMX L−1 in the mixture after 12 days of cultivation. The greater biodegradation observed at higher SMZ and SMX concentrations indicates that microalgal degradation of SMZ and SMX could act as an efficient adaptive mechanism to antibiotics.
•S. obliquus can withstand high doses of SMZ and SMX.•EC50 of SMZ, SMX and their mixture for S. obliquus was 1.23, 0.12, and 0.15 mg L−1.•S. obliquus removed 62.3 and 46.8% of SMZ and SMX, respectively.•A greater biodegradation was observed in higher SMZ and SMX concentration.
Various compositions of Cs promoted Mn catalysts were synthesized and investigated for selective oxidation of 5-HMF to DFF, among which Mn-Cs(80:20) was found to be most efficient giving 91 % ...conversion of 5-HMF and 99 % selectivity to DFF. Detail characterization like N2-sorption, BET surface area, TG-DTA, XRD, XPS, FE-SEM-EDX, TEM, HR-TEM, CO2-TPD, H2-TPR, O2-TPO, FTIR, Raman spectra and CH3OH-IR were done to establish structure-activity correlation. Enhanced surface area, porosity, thermal stability, dual morphologies were observed due to inclusion of Cs in Mn lattice domain which further enhanced the crystallinity, and oxygen diffusion on the surface. Mixed morphologies comprising nanoparticles (4–5 nm) and nanocubes (50–60 nm) were observed with enhanced redox potential and reduced work function due to weakening of Mn-O bonds. Significant increase in the basicity of catalyst, interfacial redox properties and lattice oxygen led to highly efficient oxidation of 5-HMF to DFF via Mars-van Krevelen mechanism at relatively milder conditions i.e. T = 90 °C and PO2= 200 psig. The catalyst was easily recyclable up to 7 times with minor loss in activity which was regenerated heat treatment protocol.
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•Catalytic selective and efficient catalytic oxidation of 5-HMF to DFF.•Mn-Cs(80:20) catalyst developed with dual morphology.•Surface Brönsted basicity was identified by means of CO2-TPD and CH3OH-IR.•Increased oxygen defect identified by XPS which led to enhanced catalytic activity.•Oxidative dehydration occurred by Mars-van Krevelen mechanism.
