Low Carbon Deposition Research Articles

Fluidized bed reforming of methane by chemical looping with cerium oxide oxygen carriers

Methane reforming is an industrial process for hydrogen production having a high CO2 footprint that can be mitigated either by using renewable methane, or by recycling carbon dioxide from capture. Methane reforming assisted by an oxygen carrier was currently investigated, being an attractive option for production of hydrogen and carbon monoxide mixtures. The distinctive aspect of present research was the development of three different granular materials based on CeO2 to be used in fluidized beds, obtained by pelletization and calcination at 900 and 1200 °C of CeO2 or CeO2/Al2O3 powder. Fluidization and abrasion tests were performed at cold and hot conditions, showing the best attrition resistance of materials calcined at the highest temperature, with attrition rate equal to 0.3 %/h. Conversely, thermogravimetric tests at 900 °C revealed the best performance of CeO2 granules sintered at lower temperature with respect to the others in terms of oxygen supply capacity, achieving 0.55 of conversion degree. Reforming and regeneration cycles were performed in fluidized bed at 940 °C with CeO2/Al2O3 granules, providing instantaneous methane conversion up to 37 %, high carrier conversion (0.87) and low carbon deposition (2.9 mg/g) during the reforming step.

Evaluation of La1−xSrxNi0.4Fe0.6O3-δ as Electrode Materials for Direct Methane Symmetrical Solid Oxide Fuel Cells

In this work, La1−xSrxNi0.4Fe0.6O3-δ (0 ≤ x ≤ 0.2) oxides were synthesized and employed as the identical electrode of direct methane symmetrical solid oxide fuel cell (SSOFC). In addition, the phase structure, redox stability, electrical conductivity, chemical compatibility, and thermal expansion of La1−xSrxNi0.4Fe0.6O3-δ oxides were evaluated. The La2NiO4 phase occurs when the amount of doped Sr rises to 0.2. The composition of La0.9Sr0.1Ni0.4Fe0.6O3-δ (LSNF9146) boasts the highest conductivity of 463 S cm−1 with lowest activation energy of 0.066 eV as well as a relatively large thermal expansion coefficient. After treatment in methane for 10 h, the LSNF9146 oxide exhibits 33% lower carbon deposition than the LaNi0.4Fe0.6O3-δ (LNF46) oxide. Moreover, the impregnated LSNF9146 electrode demonstrates lower polarization resistance in both air and methane atmospheres. SSOFCs with impregnated LSNF9146 and LNF46 identical composite electrodes have the maximum power densities of 233 and 170 mW cm−2 at 850 °C in methane, respectively. These results prove that LSNF9146 is a promising symmetrical electrode with high catalytic activity, good redox stability, and coking resistance to direct methane SSOFCs.

Study on the mechanism of syngas production from catalytic pyrolysis of biomass tar by Ni–Fe catalyst in CO2 atmosphere

This study focused on the pyrolysis behavior of biomass tar (toluene as model compound) via Ni-Fe catalyst, and enhanced the generation of syngas in the CO2 atmosphere. The whole reaction was carried out in a two-stage fixed-bed reactor. The evolution and yield of H2, CO, total syngas, and carbon deposition were investigated by Fe loading, catalyst dosage, pyrolysis temperature, and CO2 flow rate. The results showed the catalytic pyrolysis process of toluene obtained a gas yield of 323.3 mL/g-toluene, H2 yield of 181.7 mL/g-toluene, and carbon deposition of 794.3 mg/g-catalyst with Ni-4 %Fe/HZSM-5 catalyst dosage of 16 % at 900 ℃ for 40 min. Specifically, the catalytic pyrolysis process of toluene produced 27.43 % higher total syngas, 23.52 % higher H2, 66.0 % lower carbon deposition, and 391.67 % higher CO (19.07 mL/g-toluene) in the CO2 atmosphere with 40 mL/min. Approximately 4.43 g (21.22 mL) of CO2 was consumed by pyrolysis of 1 g toluene to generate the total syngas. This provides a theoretical basis for the synergistic pyrolysis of biomass tar and CO2 in the pyrolysis/gasification process of biomass, expounds the synergistic effect of Ni–Fe/HZSM-5 catalyst and CO2, reduces greenhouse gas emissions, and realizes the recycling of resources.

Inhibition of sintering and coking by post-coating group IIA metal oxides on trace-Rh-promoted Ni-based catalysts for high-temperature steam reforming

Liquid hydrocarbon steam reforming (SR) faces the challenges of sintering and carbon deposition induced deactivation of catalysts. Herein, the strategy for stabilizing trace Rh-promoted Ni-based catalysts by post-coating group IIA metal oxide is proposed. The stabilities for catalytic n-dodecane SR are as followed: Mg–Rh–Ni–CZO > Sr–Rh–Ni–CZO > Ba–Rh–Ni–CZO ∼ Ca–Rh–Ni–CZO ∼ Rh–Ni–CZO. The reduction suppression of Rh–Ni by alkaline-earth metal oxide and the formation of Mg–O–Ni bonds in Mg–Rh–Ni–CZO are demonstrated by TPR and EXAFS techniques. The TEM and TGA characterization results confirm that IIA metal oxide inhibit Ni sintering, in turn decreasing the carbon deposition amount and graphitic carbon proportion. Negligible Ni sintering and low carbon deposition (0.7 mg/g-cat.·mmol-C12H26) occurs in Mg–Rh–Ni–CZO after SR at 700 °C for 50 h. Contrarily, the MgO-precoated Rh–Ni–Mg–CZO do not exhibit improved catalytic performance owing to the correlation between sintering and coking behaviors with interfacial structures.

Ni-phyllosilicate nanotubes coated by CeO2 for ultra-efficiency of 36.9% and near-limit CO2 conversion in solar-driven conversion of CO2-to-fuel

Solar-driven CO2 reduction by methane (CRM) into valuable syngas not only mitigates greenhouse gases but also provides high-value syngas. However, it is still a daunting challenge to achieve high solar-to-fuel efficiency and good durability simultaneously. Here, a novel strategy of direct photothermocatalytic CO2 is proposed based on a unique nanocomposite of ceria coated Ni-phyllosilicate nanotubes (Ni-psnts@CeO2). A record-high solar-to-fuel efficiency (36.9 %) with very high production rates of H2 and CO (120.90 and 136.84 mmol gcat min−1) and high CO2 conversion rate (90.4 %) close to thermodynamic limit are demonstrated. Excellent long-term durability is achieved due to its extremely low carbon deposition rate of 1.3 × 10−4 gc gcat h−1 under focused UV–vis-IR irradiation for 100 h. These high performances are partially attributed to the active involving of lattice oxygen and oxygen vacancies from ceria in carbon gasification and CO2 activation, which are confirmed by 18O isotope labeling and In-situ DRIFTS measurements. In addition, decreased activation energy enabled via photoactivation effects from photoexcited hot electrons also benefits high activities under direct light illumination. This work offers novel approaches for highly efficient and stable solar-driven CO2-to-fuel conversion.

CeO2 Nanorod@NiPhy Core‐shell Catalyst for Methane Dry Reforming: Effect of Simultaneous Sintering Prevention of CeO2 Support and Active Ni

AbstractPreventing the sintering of nano‐catalyst is crucial to maintain their performance especially for high‐temperature reactions such as CO2 reforming of methane (DRM) reaction. In this paper, we design CeO2 nanorod@Ni phyllosilicate (CeO2@NiPhy) catalysts with different NiPhy shell thickness to simultaneously preserve the morphology of CeO2 nanorod and prevent the sintering of Ni. Compared with Ni/CeO2 supported catalyst, CeO2@NiPhy core‐shell catalyst with a shell thickness of 9 nm exhibits much better performance for DRM with stable CH4 and CO2 conversions of 75 % and 80 % respectively and lower carbon deposition due to high Ni sintering resistance and higher thermal stability of CeO2 during calcination and DRM reaction thereby higher oxygen vacancies concentration. In‐situ diffuse reflectance infrared Fourier transform spectra result demonstrates that DRM reaction takes place with a bi‐functional mechanism on CeO2@NiPhy. This design strategy can be applied to prepare other nano‐catalysts with high sintering resistance of both active metal and catalyst support for high‐temperature applications.

Catalytic conversion of toluene by biochar modified with KMnO4

This study aims to investigate the effects of biomass species, modification treatment, experimental time and atmosphere on the catalytic conversion of toluene (tar model compound) by biochar from gasification of oak, wheat straw and Enteromorpha. The gas and liquid phase products are detected by GC and GC–MS, respectively. The physical and chemical characteristics of biochar samples are analyzed by SEM-EDS, BET, XRD and XPS. The results show that the catalytic activity of oak char modified by KMnO4 (Mn-OC) is higher than that of other biochar samples. The KMnO4 modification improves the pore structure, increases oxygen-containing groups and enhances the activity of oak char. The relatively high toluene conversion rate (53.96 %) and low carbon deposition rate (3.41 %) of Mn-OC indicates that KMnO4 is more suitable for the modification of oak char. H2 and aromatic hydrocarbons (especially biphenyl and their derivatives) are the main components of gas and liquid products, respectively. The proportion of H2 in the total volume of H2, CO, CH4 and CO2 of Mn-OC reaches 56.94 %. The addition of water vapor is helpful to the formation of oxygen-containing groups and the improvement of biochar surface structure. Thus, adding moderate water vapor is beneficial to promote the catalytic activity of biochar. The toluene conversion rate and the total volume fraction of four main gases decrease with the increase of experimental time. They reduce significantly when the experimental time is longer than 120 min, from 44.51 % (120 min) to 24.86 % (180 min), which might be due to the damage of pore structure and the consumption of oxygen-containing functional groups.

Improved benzene selectivity for methane dehydroaromatization via modifying the zeolitic pores by dual-templating approach

Catalytic upgradation of methane into benzene and valuable chemicals over Mo/HZSM-5 has a great economic potential, yet it has serious drawback due to the obstacles in the micropores because of extensive coking at an elevated temperature during methane dehydroaromatization (MDA). Under such circumstances, it requires the design of micro/mesoporous ZSM-5, which has the advantages viz. enhanced product formation due to uniform Mo distribution inside the pores and lower carbon deposition because of improved mass transfer rate within the hierarchical pores. We infer herein a unique strategy to control the porous structures of ZSM-5 through a dual templating approach, employing both C6 and C12 -surfactants as porogen. The structural and morphological parameters of the synthesized ZSM-5 catalysts were investigated in detailed to ascertain the crystallinity, porosity, particle shape, size, Si/Al ratio, and acid strength which were further correlated with the physicochemical and catalytic properties of Mo modified HZSM-5 catalysts. After Mo impregnation, all the catalysts were evaluated for methane dehydroaromatization reaction. Compared with the conventional Mo/HZSM-5(C), C6 surfactant-treated hierarchically porous Mo/HZSM-5(H) showed the highest benzene formation rate (1.5 μmol/gcat. s) and longer stability of 270 min in TOS analysis. In contrary, C12 surfactant modified Mo/HZSM-5(D) is inferior towards MDA reaction (benzene formation rate: 0.5 μmol/gcat. s). We attribute to the difference in MDA reaction could be due to the hierarchically mesoporous feature of Mo/HZSM-5(H) with interconnected topology that precludes secondary reaction of coking from benzene and hence, contributing significant stability towards MDA reaction.

Performance of pulsed plasma thrusters with a non-volatile liquid propellant stored in porous ceramics with different pore diameters

Pulsed plasma thrusters (PPTs) typically have characteristics like a high specific impulse, a small volume, a low system mass when used in microsatellites. However, the lifetime of these thrusters is limited by their disadvantages, which include carbon deposition. A non-volatile liquid perfluoropolyether showed a good capability of lower carbon deposition in previous studies, but previous investigations focused on carbon deposition. The influence of the pore diameter of porous ceramics, which can change the supply rate, has not yet been studied. Perfluoropolyether, which is impregnated into the porous ceramics with different pore diameters (10 nm, 100 nm, 1 μm), was investigated in this study. A decreasing pore diameter of porous ceramics resulted in a lower resupply rate to reduce the ablated mass bit (the consumption of propellant per discharge) of PPTs. The use of perfluoropolyether resulted in an increase in the ablated mass bit and impulse bit, and a decrease in the specific impulse and efficiency. When using perfluoropolyether, the impulse bit increases with decreasing pore diameter of the porous ceramic. Perfluoropolyether achieved a higher specific impulse and efficiency with decreasing pore diameter of the porous ceramic, due to the increasing kinetic energy of plasma as a percentage of total energy.

Benchmarking Cu/BEA and HBEA catalysts for high-octane gasoline synthesis

We distinguish rates at which carbon deposition occurs during initiation, rates at which catalytic centers are lost during deactivation, and paraffin-to-olefin ratio during propagation as benchmarks that distinguish 5 wt% Cu/H-BEA and H-BEA (Si/Al = 13.5) catalysts during dimethyl ether (DME) homologation in the presence of hydrogen. Studies that systematically vary initial DME contact time (210, 94, and 45 molH+, initial s (mol C)−1), DME pressure (4 and 22 kPa), and H2 pressure (1, 24, and 48 kPa) reveal that Cu enables lower carbon deposition rates (on a per proton basis) in the induction period, increases the effluent paraffin-to-olefin ratio during propagation, and decreases instantaneous site-loss yields during termination by 1.5–2× (moles of active sites lost per mole of DME) thus augmenting the degree of product saturation and catalyst stability during DME homologation. These results provide mechanistic insights revealing the critical role of Cu in facilitating DME homologation to high value, high-octane gasoline-range hydrocarbons with higher cumulative turnovers than proton form H-BEA.

An all-in-one zeolite@Ru–Al2O3 nanoplatform toward highly efficient, anti-coking, and recyclable hydrocarbon cracking catalysis

Efficient utilization of hydrocarbon fuels holds great significance for the current vehicle low-emission requirements and future carbon-neutral society. However, the scenario that limits the effective fuel use and combustion is the present undesirable hydrocarbon-cracking catalysts of low activity, serious coking, and easy degradation. To tackle these issues, we rationally designed and synthesized an active, anti-coking, and recyclable all-in-one zeolite@Ru–Al2O3 catalyst on FeCrAl support by steam-assisted crystallization and atomic layer deposition. Ru nanoclusters dispersedly on ZSM-5 can boost the catalytic efficiency for hydrocarbon cracking and anti-coking, while the protective Al2O3 thin layers further ensure the reusable economy. As for n-dodecane (C12H26) cracking reaction, the ZSM-5@Ru–Al2O3 showed a high unit activity up to 0.1253%·ml·mg−1·min−1, low-carbon deposition rate, and the enhanced first-cycle carbon removal rate of 78.3% for recyclable use. Density functional theory (DFT) calculations have further confirmed that high catalytic efficiency and low-carbon deposition benefit from the timely adsorption of C12H26 and timely transfer of reactant products at the composite interface. This work opens interesting possibilities for the rational design and fabrication of high-efficient, anti-coking, and recyclable hydrocarbon cracking catalysts through multifunctional structural regulations.

High Fuel Yields, Solar‐to‐Fuel Efficiency, and Excellent Durability Achieved for Confined NiCo Alloy Nanoparticles Using MgO Overlayers for Photothermocatalytic CO2 Reduction

Solar‐energy‐driven CO2 reduction to produce fuel is of great importance for alleviating the greenhouse effect and energy shortage. Here, a composite of MgO overlayers confined NiCo alloy nanoparticles supported on MgO (NiCo@MgO/MgO) is prepared. Extremely high production rates of H2 (rH2) and CO (rCO) (112.98 and 127.13 mmol min−1 g−1, respectively) and large solar‐to‐fuel efficiency (η, 39.3%) are achieved on NiCo@MgO/MgO for photothermocatalytic CO2 reduction by CH4 under ultraviolet–visible–infrared (UV–VIS–IR) illumination. The high fuel production rates and η originate from efficient light–thermal conversion and photoactivation, which can boost the photothermocatalytic activity by reducing the activation energy. Importantly, NiCo@MgO/MgO does not show deactivation during a 90 h photothermocatalytic CO2 reduction by the CH4 durability test, owing to its low carbon deposition rate. Experimental evidence reveals that the NiCo alloy and MgO overlayers can inhibit CO disproportionation and accelerate the oxidation of carbon species, thereby significantly decreasing the carbon deposition rate.

Controllable synthesis of xPt–yNiO/MgO–PWAC nanoparticles and high-efficiency conversion for CO2/CH4 reforming reaction

Utilization and conversion of CO2 through dry reforming of methane to syngas have attracted very great attention because of china's action plans of carbon neutrality to cut net CO2 emissions to peak by 2030. Hence, we designed/prepared a series of high-performance xPt–yNiO/MgO–PWAC (Persimmon Wood-derived Activated Carbon) nanoparticle catalysts via polyol technique. Its catalytic performance and stability were evaluated for CO2/CH4 reforming reaction at 700–800 °C. The experimental results demonstrated that initial conversions of CO2 and CH4 over 1.5Pt11NiO/MgO–PWAC catalysts were 96% and 95.3%, respectively, higher than those observed over 11NiO/MgO–PWAC due to a fact the appreciate Pt loadings will significantly improve the dispersion of Ni/Pt nanoparticles and suppress the formation of coke on the active sites of nickel nanoparticles effectively. The results of HRTEM, TG–DSC XRD, CO2-TPD, and XPS studies revealed that high catalytic performance of catalyst correlated closely with the size and dispersion of metal nanoparticles, the preferred properties of CO2 adsorption as well as low carbon deposition on the interface between active Ni sites/MgO-PWAC supports.

Advanced Steam Reforming of Bio-Oil with Carbon Capture: A Techno-Economic and CO2 Emissions Analysis

A techno-economic analysis has been used to evaluate three processes for hydrogen production from advanced steam reforming (SR) of bio-oil, as an alternative route to hydrogen with BECCS: conventional steam reforming (C-SR), C-SR with CO2 capture (C-SR-CCS), and sorption-enhanced chemical looping (SE-CLSR). The impacts of feed molar steam to carbon ratio (S/C), temperature, pressure, the use of hydrodesulphurisation pretreatment, and plant production capacity were examined in an economic evaluation and direct CO2 emissions analysis. Bio-oil C-SR-CC or SE-CLSR may be feasible routes to hydrogen production, with potential to provide negative emissions. SE-CLSR can improve process thermal efficiency compared to C-SR-CCS. At the feed molar steam to carbon ratio (S/C) of 2, the levelised cost of hydrogen (USD 3.8 to 4.6 per kg) and cost of carbon avoided are less than those of a C-SR process with amine-based CCS. However, at higher S/C ratios, SE-CLSR does not have a strong economic advantage, and there is a need to better understand the viability of operating SE-CLSR of bio-oil at high temperatures (>850 °C) with a low S/C ratio (e.g., 2), and whether the SE-CLSR cycle can sustain low carbon deposition levels over a long operating period.

B-Ni/MgAl2O4 catalyzed dry reforming of methane: The role of boron to resist the formation of graphitic carbon

The present contribution reports a single-step synthesis of B(x)-Ni/MgAl2O4 (where x = 1%, 3%, and 5% wt.%) via the NaBH4 reduction for dry reforming of methane (DRM) and investigates the effect of B promotion. Characterization (ICP-OES, XRD, H2-TPR, XPS, HR-TEM with EDS and HAADF) results suggested B incorporation facilitates the formation of Ni0 and Ni-B species and smaller Ni particle size (∼7 nm) compared to unpromoted catalyst. The results of the DRM reaction indicated that ∼ 2.8 wt% B-containing catalyst (B(3)-Ni/MgAl2O4) exhibited maximum activity and minimum decline in conversion (%) for both reactants (CH4 and CO2). The Turnover frequency (TOFCH4) observed for the B(3)-Ni/MgAl2O4 is ∼ 2.6 times higher than the non-B catalyst. The investigation of spent catalysts confirms the insignificant deactivation due to the absence of graphitic carbon. The carbon formation is (∼11.2 times) lesser for B(3)-Ni/MgAl2O4 than for the non-B catalyst. The enhanced activity and low carbon deposition for B (∼2.8 wt%) containing catalyst attributed to the occupancy of B in octahedral sites of the Ni-sub surface, which restricts the crystalline growth leading to a smaller Ni particle size, stabilize the metallic state of Ni, and affect the Ni-C interaction during DRM.

Synthesis gas and H2 production by chemical looping reforming using bio-oil from fast pyrolysis of wood as raw material

• CLR of pine wood bio-oil has been demonstrated in a 1 kW th continuous unit. • Complete conversion of bio-oil was found during 60 h of operation. • Carbon deposition can be minimized and controlled in the continuous CLR unit. • Maximum H 2 production and H 2 /CO ratio were found at 650 °C with very low C deposition. • Auto-thermal H 2 production at 650 °C was 13.6 g/100 g of bio-oil with H 2 O/bio-oil = 6. The interest of using bio-oil produced by biomass fast pyrolysis to generate H 2 and high value chemicals is growing up in order to reduce CO 2 emissions by the use of biomass. In the present work, bio-oil Chemical Looping Reforming was demonstrated in a 1 kW th continuous unit during 60 h of operation using a Ni-based oxygen carrier to produce syngas/H 2 . No agglomeration of the oxygen carrier was detected. Complete conversion of the bio-oil was obtained in all cases, obtaining as main products H 2 , CO, CO 2 and in much lower concentration CH 4 . Carbon deposition in the bed appeared in almost all the experiments carried out during the bio-oil reforming, and CO 2 was found in the air reactor outlet, although did not affect to the process performance when oxygen carriers were used. This fact only let to a reduction of the CO 2 capture efficiency. Fuel reactor temperature was a key factor for the H 2 production, the H 2 /CO ratio and the carbon accumulated in the CLR unit. The maximum H 2 production together with the maximum H 2 /CO ratio of 6 were found at the lowest temperature used, 650 °C. In addition, the carbon formed in the fuel reactor was reactive enough so that it could be burnt in the air reactor with minimum accumulation in the continuous unit. The autothermal H 2 production was 13.6 g/100 g of bio-oil without water at 650 °C with a H 2 O/bio-oil = 6, which corresponds to 68 mol H 2 /kg of bio-oil without water. Therefore, the CLR process of bio-oil allows obtaining high H 2 production with low carbon deposition at 650 °C using less amount of water than in conventional bio-oil reforming.

A two step Microwave-assisted coke resistant mesoporous Ni-Co catalyst for methane steam reforming

Methane steam reforming (MSR) is an assuring reaction using steam to produce H2 as clean energy over a nicκel-based catalyst. We synthesized mesoporous monometallic NiMgAl2O4 and bimetallic NiCoMgAl2O4 catalysts in a two-step combustion method using a mix of fuels and powder metallurgy. BET-BJH, XRD, TGA, TPR, FESEM, and EDX-mapping characterized surface area, porosity, morphology, crystalline structure, and metal-support interaction behavior. The products exhibited strong interaction of well-structured MgAl2O4 spinel with NiO , in both specimens. The MSR evaluation tests at 750 °C under atmospheric pressure, CH4:H2O feed ratio of 1:1.2 showed the bimetallic catalyst has the highest conversion of 99.30% with low carbon deposition(0.09% weight loss), after 15 h. Both catalysts demonstrated a miniature nickel particle sintering. TG analysis revealed 0.0059 and 0.0035 mg lamentous carbon deposited on 3.4820 mg NiMgAl2O4 and 3.4820 mg NiCoMgAl2O4, respectively. Also, no XRD diffraction peaks related to the lamentous carbon were observed. Moreover the carbon balance showed the higher recovery of carbon (close to 1) for Co-promoted catalyst. Highly dispersed active Ni species might be responsible for high catalyst activity and resistant to coking in the MSR reaction.

Enhanced conversion efficiency and coking resistance of solid oxide fuel cells with vertical-microchannel anode fueled in CO2 assisted low-concentration coal-bed methane

Clean and efficient utilization of the abundant low concentration coal-bed methane (LC-CBM) via solid oxide fuel cells (SOFCs) is highly attractive for saving energy and mitigate the emission of greenhouse gases. However, it still remains a great challenge because of the low conversion efficiency and carbon deposition. Herein, an improvement strategy is proposed via incorporating dry reforming reaction of CO2 assisted LC-CBM. By introducing CO2 in LC-CBM, the methane conversion improves significantly. A maximum methane conversion is achieved by incorporating 5 %CO2 and the value is increased from 31.69% to 50.03%. Meanwhile, a high CO2 conversion of 74.58% is also achieved. The maximum power density of the single cell with vertical-microchannel anode fueled with 5 %CO2 in LC-CBM is 1321.5 mW cm−2 at 800 °C, which is a bit lower than that without CO2 participation. This is probably ascribed to the open circuit voltage decrease caused by the increased partial pressure of oxygen at anode. The coking tolerance of the single cell with CO2 participation can be improved owing to the high conversion efficiency, leading to a stable power output performance. CO2 assisted LC-CBM for SOFCs provides a potential solution for the efficient conversion of the low calorific value fuels.

Formation and assessment of ecological risks of urban landscapes in industrial cities of Belarus

The problems of the formation of hazardous natural and man-made processes in industrial cities, contributing to the emergence of environmental risks, are presented. To date, an extensive literary material has been accumulated on this problem, concerning the causes of its occurrence, analysis of the patterns of development, and the possibilities of managing risks, including the environmental ones. It has been established that the list of reasons for the formation of risks in cities lacks one of the most important factors that we have discovered – the structure of urban landscapes, which are quite large objects of urban development. To identify the role of these objects in the formation of environmental risks, the cities of Orsha and Pinsk were selected. These cities were laid down almost simultaneously at the beginning of the 11th century, but they have a different history of development. Maps of urban landscapes of cities were compiled, geochemical studies of their soil cover were carried out, geochemical and thermal anomalies of the surface were revealed, the volumes of ecosystem services (carbon absorption) by green spaces were calculated. It was found that urban landscapes perform various functions in the system of environmental risks: some of them contribute to the development of hazardous processes, others – to mitigate them. So, soil pollution with heavy metals (with an excess of the content of Pb, Cr and Cu over the MPC by 1.2–5.6 times in Pinsk), the strongest heating of the surface (8–16 °C higher than the air temperature in Pinsk and Orsha) and low carbon deposition (100–500 t per year) are typical for urban landscapes of the historical center, urban landscapes with a predominance of industrial buildings, urban landscapes for complex residential multi-storey, public and industrial buildings. Urban landscapes, in the structure of which there are elements of landscape and recreational areas of public use (parks, forest parks, squares), as well as agricultural lands and water bodies, are characterised by a low content of heavy metals in soils (below the MPC in Pinsk, below the background in Orsha), low surface temperature (2–3 °C higher than the air temperature), high volume of carbon deposition (2.6–2.8 thsd t per year). An assessment of the probability of risks associated with the described processes was carried out, which helped to find out that they correspond to the categories of «acceptable» and «neglected», options for risk management were proposed.

Synthesis of Ni@Al2O3 nanocomposite with superior activity and stability for hydrogen production from plastic-derived syngas by CO2-sorption-enhanced reforming

Catalytic dry (CO2) reforming of plastic-derived syngas is a promising method of producing hydrogen-rich syngas and reducing greenhouse gases. The development of catalysts with high activity and stability is critical for this reaction. In this study, we fabricated core-shell structured Ni@Al2O3 catalysts with different shell thicknesses using advanced polyol and sol-gel methods. The effects of different Al/Ni ratios on the activity and stability of the catalysts in the CO2 reforming reaction were investigated. The main challenge for CO2 reforming of methane is carbon deposition. In the developed catalysts, the mesoporous Al2O3 coating outside the Ni core enhances the stability. However, the interaction between the core and the shell strongly affects the catalyst activity and product selectivity in the reaction. The catalyst with an Al/Ni ratio of 2 exhibited the highest methane conversion of up to 88% and the lowest carbon deposition, compared to the congeners with Al/Ni ratios of 1 and 3.