Current society is inherently based on liquid hydrocarbon fuel economies and seems to be so for the foreseeable future. Due to the low rates (photocatalysis) and high capital investments ...(solar-thermo-chemical cycles) of competing technologies, reverse water gas shift (rWGS) catalysis appears as the prominent technology for converting CO
2
to CO, which can then be converted
via
CO hydrogenation to a liquid fuel of choice (diesel, gasoline, and alcohols). This approach has the advantage of high rates, selectivity, and technological readiness, but requires renewable hydrogen generation from direct (photocatalysis) or indirect (electricity and electrolysis) sources. The goal of this review is to examine the literature on rWGS catalyst types, catalyst mechanisms, and the implications of their use CO
2
conversion processes in the future.
The reverse water gas shift reaction, its proposed mechanisms, currently used and proposed catalysts and an intensified version of the reaction are evaluated for their abilities to significantly reduced CO
2
atmospheric concentration.
Our objective was to update the EULAR recommendations for the management of systemic lupus erythematosus (SLE), based on emerging new evidence. We performed a systematic literature review ...(01/2007-12/2017), followed by modified Delphi method, to form questions, elicit expert opinions and reach consensus. Treatment in SLE aims at remission or low disease activity and prevention of flares. Hydroxychloroquine is recommended in all patients with lupus, at a dose not exceeding 5 mg/kg real body weight. During chronic maintenance treatment, glucocorticoids (GC) should be minimised to less than 7.5 mg/day (prednisone equivalent) and, when possible, withdrawn. Appropriate initiation of immunomodulatory agents (methotrexate, azathioprine, mycophenolate) can expedite the tapering/discontinuation of GC. In persistently active or flaring extrarenal disease, add-on belimumab should be considered; rituximab (RTX) may be considered in organ-threatening, refractory disease. Updated specific recommendations are also provided for cutaneous, neuropsychiatric, haematological and renal disease. Patients with SLE should be assessed for their antiphospholipid antibody status, infectious and cardiovascular diseases risk profile and preventative strategies be tailored accordingly. The updated recommendations provide physicians and patients with updated consensus guidance on the management of SLE, combining evidence-base and expert-opinion.
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•Low temperature (600 °C) CO2 conversion via reverse water gas shift chemical looping.•Stable operation for several conversion cycles – promising for industrial ...application.•Perovskite oxides with three transition metals in B-site demonstrate CO2 conversion.•Role of transition metals (Fe, Co, Mn) explored through multiscale approach.•Preferential surface segregation of Co and Fe found favorable for CO2 conversion.
Perovskite oxides of the form ABO3 have shown substantial promise in reverse water gas shift chemical looping (RWGS-CL) process for low temperature thermochemical CO2 conversion to CO. Transition metals on the ‘B’ site of these perovskite oxides hold the key to tuning the material properties essential for efficient CO2 conversion. The role of Co, Fe and Mn in LaBO3 has been investigated through a combined theoretical and experimental approach. Intrinsic oxygen vacancy formation characteristics of these materials and the electronic charge distribution were explored via ab-initio density functional theory (DFT) simulations, while the microscale properties like crystallite size and CO2 conversion yield were probed experimentally. Through this multiscale study, the material properties that govern the stable and enhanced CO2 conversion phenomenon by Fe rich perovskites as opposed to Co and Mn rich phases are differentiated.
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•La0.75Sr0.25FeO3 perovskite oxide combined with various supports and evaluated for thermochemical CO2 conversion.•SiO2 support enhanced CO yield by 150% compared to unsupported ...perovskite after reduction at 600 °C.•Enhancement by silica support caused by restructuring that increased perovskite oxide surface area.•Some support lowered perovskite oxide performance due to overgrowth.
Perovskite-type oxides show clear potential for thermochemical solar-driven CO2 conversion. These materials exhibit the exact characteristics (e.g., structural endurance and high oxygen redox capacity and exchange kinetics) required by the low temperature reverse water-gas shift chemical looping process. In this study, the La0.75Sr0.25FeO3 (LSF) perovskite oxide was combined with various supports, including popular redox materials CeO2 and ZrO2 along with more abundant alternatives such as Al2O3, SiO2, and TiO2, for potential application at industrial scale. Supporting LSF on SiO2 by 25% mass resulted in the largest increase of 150% in CO yields relative to unsupported perovskite after reduction at 600 °C. This is a result of significantly reduced perovskite oxide particle size confirmed by SEM/TEM imaging and crystallite size from Scherrer analyses of XRD patterns. Due to solid-state reactions, minor secondary phases were observed at the LSF:support interface when using SiO2 or TiO2. Oxygen vacancy formation occurred only on the perovskite oxide phase, as suggested by low temperature experiments and consistent with density functional theory calculations. The role of each metal oxide support towards suppressing or enhancing the CO2 conversion is elucidated. Through utilization of SiO2 as support, the reverse water-gas shift chemical looping process using perovskite-based composites was significantly improved.
A technoeconomic analysis (TEA) and life cycle assessment (LCA) was conducted on the use of landfill gas (LFG) for electricity generation using an internal combustion engine. This study provides ...insights that can guide LFG waste to energy (WTE) operators on decisions concerning installation of contaminant removal from LFG for electricity generation. Four scenarios were analyzed; the first (Scenario 1) was a facility with a single siloxane removal unit (SREU) sized for 6 months of continuous use, the second (Scenario 2) was a facility with parallel SREUs sized for one month of use, the third (Scenario 3) was a facility with no SREU, and the fourth was a facility that flared all LFG captured. The TEA revealed that the chiller cost was over 50% the total purchase cost of the LFG pre-treatment system. When the complete LFG to electricity process was analyzed, the internal combustion engine had the highest percentage of total capital investment and the total annual cost. For the base case, it became economically beneficial to install a SREU at facilities with LFG flowrates greater than ∼2000 m3/h. Sensitivity analysis showed that at a base case of 1700 m3/h, LFG (50% CH4), and 50 mg/m3 D4, the net income of facilities in Scenarios 1 to 3 became positive at an electricity sales price greater than 5.5 cents/kWh. LCA revealed that Scenario 2 had the greatest CO2 emission reduction. Scenario 3 is observed to save less CO2 emissions as biogas flowrate increases due to frequent engine shutdowns. Although there are differences in the global warming potential (GWP 100) for Scenarios 1 to 3, with Scenario 2 being the best and Scenario 3 being the worst, the differences are very small. For this reason, economics alone are sufficient in decision making.
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•TEA and LCA conducted on LFG to electricity with and without pretreatment.•Siloxane removal unit economical in facilities with LFG flowrates over 2000 m3/h.•Siloxane removal units with continuous operation results in lowest CO2 emissions.•Source of avoided electricity on the global warming potential (GWP) was analyzed.
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► Ni–MgO–(Ce,Zr)O2 catalysts optimized for tri-reforming. ► Ni:Mg and Ce:Zr ratios important to limit coking. ► Ideal formulation was Ce0.6Zr0.4O2–8Ni8Mg prepared by wet impregnation. ...► Optimized gas feed ratios were CH4:CO2:H2O:O2=1:0.7:0.5:0.2. ► Hydrogen-to-carbon monoxide ratio increased with space velocity.
This paper highlights the performance of Ni–MgO–(Ce,Zr)O2 tri-reforming catalysts under various reaction conditions and explains results using catalyst characterization. Testing under controlled reaction conditions and the use of several catalyst characterization techniques (BET, XRD, TPR, SEM-EDS, and XPS) were employed to better explain the effects of the synthesis parameters on the reaction performances. The support Ce:Zr ratio, metal loading techniques, metal wt%, and Ni:Mg ratios all had a pronounced influence on the catalyst performance. An even ratio of Ce:Zr for the support and an even ratio of Ni:Mg gave the best performance. The wet impregnation method consistently showed more resistance to coke formation when compared to the deposition precipitation method, but the difference was attributed to a better ability to load Mg by wet impregnation. Lower than previously reported H2O concentrations in the feed gas composition also led to desired H2:CO ratios needed for FT synthesis while maintaining high conversions of CO2 and resistance to coke formation. High GHSV (61,000h−1) yielded significantly higher H2:CO ratios when compared to reactions run at lower GHSV (25,000h−1). These results suggest that steam reforming reactions are kept further from equilibrium at higher GHSV and result in higher H2 production. The tested tri-reforming catalyst produced desired H2:CO ratios with minimal deactivation, high reactant conversions, and extended catalyst lifetime.
Dry reforming catalysts, especially those with activity at moderate temperatures, have been intensely investigated to enhance the conversion of biogas. Here, Ru is evaluated as a promoter for Ni-Mg ...based catalysts. Catalysts based on 1.4 wt%Ni-1.0 wt%Mg-Ce0.6Zr0.4O2 with Ru (0.02–0.32 wt%) were prepared using incipient wetness. The reducibility of the catalysts and conversions increased with increasing Ru content. Increases in conversions with increasing Ru loading was attributed to the additional active sites and synergistic effect between Ru and Ni, which weakened Ni-Mg interactions. Samples showed dry reforming activity at low temperatures (450–510 °C). Reaction rates and activation energies of higher loading Ru samples (1.4 wt%Ni-1.0 wt%Mg/Ce0.6Zr0.4 O2 with 0.16 and 0.32 wt%Ru) decreased when the reduction temperature was raised from 300 to 400 °C. A 20 h TOS study showed stable catalytic activity with minimal coke deposition. The results suggest that Ru is an alternative to Pt in promoting low temperature dry reforming of methane.
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•Zeolite shell can be used to control reactant selectivity.•Silicalite-1 shell caused diffusion limitations that vary with hydrocarbon size.•A 50 nm thick shell sufficient to wholly ...prevent reforming of heptane and toluene.•Optimum shell thickness established for hydrocarbons depending on GHSV.
The ability of a zeolite shell to enhance the selective conversion of hydrocarbons through diffusional limitations was investigated using a multi-scale model of a fixed-bed reactor. The impact of shell thickness and molecule/pore size on the catalytic performance of silicalite-1 zeolite encapsulated nickel catalyst pellets for steam reforming of C1-C7 hydrocarbons is reported. A reaction–diffusion model using kinetic expressions established in literature was employed. The model was verified through comparison with reported experimental results for steam reforming data over a temperature range of 748 – 1113 K and pressure of 1 – 10 bar. Comparisons are also made against experimental data for steam reforming in the presence of a zeolite shell. Evaluation of the Weisz-Prater criterion for both the core and encapsulated catalyst confirmed mass transfer limitation induced by the utilization of a zeolite shell. The model was used to suggest an optimal thickness that balances diffusional limitations imposed by the zeolite layer on methane versus that of the heavier hydrocarbons. The optimum thickness varied as a function of hydrocarbon size and shape which determined the diffusion rates. For toluene and heptane, a 50 nm thick shell was sufficient to wholly prevent reaction. Hydrocarbons like propane and butane required a shell 7.5 and 5 μm thick. Increasing the gas-hourly-space-velocity from 10,000 to 60,000 h-1 caused a decrease in the optimum shell thickness. This approach can be modified for application to other mixed hydrocarbon systems to predict optimal catalyst design.
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