Search Results (80)

Industrial catalysts are accelerating the global transition toward renewable energy, serving as enablers for innovative technologies that enhance efficiency, lower costs, and improve environmental sustainability. This review explores the pivotal roles of industrial catalysts in hydrogen production, biofuel generation, and biomass conversion, highlighting their transformative impact on renewable energy systems. Precious-metal-based electrocatalysts such as ruthenium (Ru), iridium (Ir), and platinum (Pt) demonstrate high efficiency but face challenges due to their cost and stability. Alternatives like nickel-cobalt oxide (NiCo₂O₄) and Ti₃C₂ MXene materials show promise in addressing these limitations, enabling cost-effective and scalable hydrogen production. Additionally, nickel-based catalysts supported on alumina optimize SMR, reducing coke formation and improving efficiency. In biofuel production, heterogeneous catalysts play a crucial role in converting biomass into valuable fuels. Co-based bimetallic catalysts enhance hydrodeoxygenation (HDO) processes, improving the yield of biofuels like dimethylfuran (DMF) and γ-valerolactone (GVL). Innovative materials such as biochar, red mud, and metal–organic frameworks (MOFs) facilitate sustainable waste-to-fuel conversion and biodiesel production, offering environmental and economic benefits. Power-to-X technologies, which convert renewable electricity into chemical energy carriers like hydrogen and synthetic fuels, rely on advanced catalysts to improve reaction rates, selectivity, and energy efficiency. Innovations in non-precious metal catalysts, nanostructured materials, and defect-engineered catalysts provide solutions for sustainable energy systems. These advancements promise to enhance efficiency, reduce environmental footprints, and ensure the viability of renewable energy technologies. Full article

Stainless steel dust (SSD) is a by-product generated during the smelting process of stainless steel, which is rich in valuable metals such as Fe, Cr, Ni, and Mn. To optimize the carbothermic reduction process of SSD, this study first conducted the thermodynamic analysis of the carbothermic reduction of SSD and then employed walnut shell biochar as a reductant with non-isothermal thermogravimetric analysis with linear heating rates of 5 °C/min, 10 °C/min, 15 °C/min, and 20 °C/min. The activation energies of the carbothermic reduction reactions were calculated using the FWO method, KAS method, and Friedman method, respectively. Subsequently, the corresponding kinetic models were fitted and matched using the Málek method. The results indicate that before 600 °C, the direct reduction of SSD by carbon plays a dominant role. As the temperature increases, the indirect reduction becomes the main reduction reaction for SSD due to the generation of CO. The activation energies calculated by the Flynn–Wall–Ozawa (FWO) method, Kissinger–Akahira–Sunose (KAS) method, and Friedman method are 412.120 kJ/mol, 416.930 kJ/mol, and 411.778 kJ/mol, respectively, showing close values and a general trend of increasing activation energy as the conversion rate increased from 10% to 90%. Moreover, the reduction reaction is staged. In the conversion range of 10% to 50%, the carbothermic reduction reaction conforms to the shrinking core model within phase boundary reactions, coded as R1/4. In the conversion range of 50% to 60%, it conforms to the shrinking core model within phase boundary reactions, coded as R1/2; in the conversion range of 60% to 90%, the carbothermic reduction reaction follows the second-order chemical reaction model, coded as F2. Full article

The application of animal manure and organic soil amendments as an alternative to expensive inorganic fertilizers is becoming more prevalent in the USA and worldwide. A field experiment was conducted on Bluegrass–Maury silty loam soil at the Kentucky State University Research Farm using the Kennebec variety of white potato (Solanum tuberosum) under Kentucky climatic conditions. The study involved 12 soil treatments in a randomized complete block design. The treatments included four types of animal manures (cow manure, chicken manure, vermicompost, and sewage sludge), biochar at three application rates (5%, 10%, and 20%), and native soil as control plots. Additionally, animal manures were supplemented with 10% biochar to assess the influence of combining biochar with animal manure on the accumulation of heavy metals in potato tubers. The study aimed to (1) determine the concentration of seven heavy metals (Cd, Cr, Ni, Pb, Mn, Zn, Cu) and two essential nutrients (K and Mg) in soils treated with biochar and animal manure, and (2) assess metal mobility from soil to potato tubers at harvest by determining the bioaccumulation factor (BAF). The results revealed that Cd, Pb, Ni, Cr, and Mn concentrations in potato tubers exceeded the FAO/WHO allowable limits. Whereas the BAF values varied among the soil treatments, with Cd, Cu, and Zn having high BAF values (>1), and Pb, Ni, Cr, and Mn having low BAF values (<1). This observation demonstrates that potato tubers can remediate Cd, Cu, and Zn when grown under the soil amended with biochar and animal manure. Full article

Biochar continues to attract growing interest as a promising soil amendment, particularly in areas contaminated with heavy metals. The present experiment was conducted on soil contaminated with zinc (Zn), copper (Cu), and nickel (Ni) in the following treatments: contamination with a single heavy metal (Zn, Cu, or Ni) and with a combination of heavy metals (ZnCu, ZnNi, CuNi, and ZnCuNi). The analysis was performed in soil samples with and without biochar addition. The biochar dose was 15 g kg⁻¹ soil. The biochar was produced from sunflower husks, with the following composition: ash—7.49%; organic carbon (C_org)—83.92%; total nitrogen (N_total)—0.91%; hydrogen—2.56%; sulfur—0.02%; oxygen—3.30%; and pH—9.79. Nickel, followed by Cu, induced the greatest decrease in Zea mays yields, whereas the smallest decline in yields was observed in response to Zn contamination. The combined application of the tested heavy metals had more damaging effects, in particular by decreasing maize yields. The values of the heavy metal impact index (IF_Hm) confirmed that heavy metals exerted a negative impact on the biochemical activity of soil. Copper applied alone and in combination with other heavy metals had the most inhibitory effect on soil enzyme activity. The toxicity of the analyzed heavy metals for plants and soil enzymes was reduced by biochar. This is confirmed by the tolerance index (TI) values for copper and nickel in Zea mays. The TI values for copper increased from 0.318 in soil without biochar to 0.405 in soil with biochar. For nickel, the TI values increased from 0.015 to 0.133. The values of the biochar impact index (IF_CB) also suggest that biochar stimulated enzyme activity in all treatments. Biochar also improved the chemical and physicochemical properties of soil, including the content of C_org and N_total and soil pH. Full article

The addition of alkaline amendments is considered an important strategy to alleviate soil acidification, with profound impacts on soil nitrogen (N) transformations such as nitrification as well as greenhouse gas (GHG) nitrous oxide (N₂O) emissions. Nitrification inhibitors (NIs) have been widely recognized to effectively mitigate N₂O emissions by depressing the nitrification process. However, the effectiveness of NIs on N₂O emissions reduction under different alkaline amendments remains largely unknown, hindering our knowledge of the optimal soil acidification mitigation strategies. In this study, the effects of NIs in combination with different alkaline amendments on N₂O emissions were assessed on typical acid soils collected from four sites during a 28-day aerobic incubation experiment. Treatments included four alkaline amendments (quicklime, chicken manure, cow dung, biochar) and no amendment control, designated as CaO, CM, CD, BC, and CK, combined with a typical NI (3,4 dimethylpyrazole phosphate, DMPP) applied at 2 mg soil kg⁻¹ or non-NI applied, respectively. Both individual amendments and their combination with DMPP significantly elevated the soil pH by 4.9–64.2% compared with the CK treatment, with the effectiveness ranking as CaO > CM ≈ CD > BC. Cumulative N₂O emissions were stimulated by the individual application of CaO, CM, and CD but were reduced by BC application compared with the CK treatment. Changes in N₂O emissions were positively correlated with the responses of the net N mineralization and nitrification rates to individual amendments, which were regulated by changes in the soil pH. The suppressive effects of NI combined with individual amendments on N₂O emissions were significant in the CaO treatment with a reduction ranging from 3.3% to 60.2%, which was attributed to decreased abundances of ammonia-oxidizing bacteria (AOB). Therefore, we concluded that the combined application of CaO and DMPP could be considered as a suitable mitigation strategy for addressing soil acidification through optimized N management. Additionally, BC can serve as a supplementary practice to simultaneously improve soil fertility. These insights are crucial for developing integrated fertilization management strategies to mitigate soil acidification with low N loss risks. Full article

Waste biomass gasification can contribute to the production of alternative and environmentally sustainable green fuels. Research at the CREC–UWO (Chemical Reactor Engineering Center–University of Western Ontario) considers an integrated gasification process where both electrical power, biochar, and tar-free syngas suitable for alcohol synthesis are produced. In particular, the present review addresses the issues concerning tar removal from the syngas produced in a waste biomass gasifier via a catalytic post-gasification (CPG) downer unit. Various questions concerning CPG, such as reaction conditions, thermodynamics, a Tar Conversion Catalyst (TCC), and tar surrogate chemical species that can be employed for catalyst performance evaluations are reported. Catalyst performance-reported results were obtained in a fluidizable CREC Riser Simulator invented at CREC–UWO. The present review shows the suitability of the developed fluidizable Ni–Ceria γ-alumina catalyst, given the high level of tar removal it provides, the minimum coke that is formed with its use, and the adequate reforming of the syngas exiting the biomass waste gasifier, suitable for alcohol synthesis. Full article

This study investigates the potential of biochars derived from agricultural waste biomass for the removal of heavy metal ions from aqueous solutions. Biochars were produced via slow pyrolysis at 793 K using almond shells (AS), walnut shells (WS), pistachio shells (PS), and rice husks (RH) as feedstocks. The physicochemical properties and adsorption performance of the resulting materials were evaluated with respect to Cd(II), Mn(II), Co(II), Ni(II), Zn(II), total Iron (Fe_tot), total Arsenic (As_tot), and total Chromium (Cr_tot) in model solutions. Surface morphology, porosity, and surface chemistry of the biochars were characterized by scanning electron microscopy (SEM), nitrogen adsorption at 77 K (for specific surface area and pore structure), Fourier-transform infrared spectroscopy (FTIR), and determination of the point of zero charge (pH_pzc). Based on their textural properties, biochars derived from WS, PS, and AS were classified as predominantly microporous, while RH-derived biochar exhibited mesoporous characteristics. The highest Brunauer–Emmett–Teller (S_BET) surface area was recorded for PS biochar, while RH biochar showed the lowest. The pistachio shell biochar exhibited the highest specific surface area (440 m²/g), while the rice husk biochar was predominantly mesoporous. Batch adsorption experiments were conducted at 25 °C, with an adsorbent dose of 3 g/L and a contact time of 24 h. The experiments in multicomponent systems revealed removal efficiencies exceeding 87% for all tested metals, with maximum values reaching 99.9% for Cd(II) and 97.5% for Fe_tot. The study highlights strong correlations between physicochemical properties and sorption performance, demonstrating the suitability of these biochars as low-cost sorbents for complex water treatment applications. Full article

Digestate as a by-product of biogas production requires appropriate utilization methods to convert it into a valuable resource. This study investigated the feasibility of using digestate from a biogas plant as a sustainable feedstock for fuel pellet production. Digestate from an agricultural biogas plant was dried and pelletized, both with and without the addition of biochar. The resulting pellets were analyzed for their physicochemical properties, elemental composition, and calorific value. Samples of pellets were examined using a calorimeter and XRF analyzer. Results showed that digestate pellets exhibited promising fuel characteristics comparable to traditional wood pellets (17.07–17.11 MJ/kg). However, the addition of biochar, while increasing calorific value, led to high ash content and elevated concentrations of Cl, S, N, Ni, Zn, exceeding acceptable limits defined by ISO 17225-6. Consequently, biochar addition is not recommended due to potential environmental concerns upon combustion. The findings highlight that digestate with initial moisture content of 7–7.5% is the most suitable for pelletization in terms of mechanical durability and strength quality. Further research is recommended to fully assess the environmental and economic viability of digestate-based fuel pellets. This approach addresses two issues: it enables waste utilization and produces a valuable resource. Full article

This study investigated the production of high-performance biochar from swine manure using a sequential carbonization process combining hydrothermal carbonization (HTC) and pyrolysis. Biochar produced through HCl-assisted sequential carbonization exhibited superior properties, including the highest fixed carbon (70.0%), higher heating value (28.48 MJ/kg, ~18.8% increase over HTC-Py), and BET surface area (279.66 m²/g, ~17 times higher than other biochars). These improvements were attributed to the catalytic role of HCl in promoting dehydration, hydrolysis, and decarboxylation, leading to a more condensed and stabilized carbon structure. Furthermore, HCl significantly enhanced heavy metal removal, reducing Zn to 343.17 mg/kg (compared to HTC-Py 1324.15 mg/kg) and lowering Cd, As, Cu, Pb, Ni, and Cr by 70–80%, demonstrating effective demineralization. This approach presents a practical strategy for producing high-quality biochar with improved carbonization, energy properties, and pollutant removal, offering potential applications in environmental and agricultural fields. Full article

The phytoremediation potential of the halophytic plant, Tamarix smyrnensis (T. smyrnensis), was examined in toxic metal spoils assisted by biochar and irrigation by air nanobubbles. The substrate (spoil) used in the present study was derived from areas close to laterite (Ni-containing ores) mines. The efficiency of biochar addition in two rates (5 t/ha and 20 t/ha) to improve microbial properties and stabilize soil aggregates was also examined. Furthermore, the effect of irrigation with air-nanobubble-supplemented water was evaluated for the remediation of toxic metal spoils. The physiological condition of the plant species was investigated in terms of biomass, height, chlorophyll content, and antioxidant enzymes. The alkali and heavy metal accumulation and their distribution in the plant parts were assessed to explore whether toxic metals could accumulate in the root and further translocate to the aboveground tissues. The growth of T. smyrnensis was not adversely affected by its cultivation in lateritic spoil, and the highest rate of biochar exhibited a beneficial effect on plant growth in terms of weight (aerial and subterranean biomass). The highest biochar application rate led to significant increases in total chlorophyll content, showing a 97.6% increase when biochar is used alone and a 136% increase when combined with nanobubble irrigation. Remarkably, only when combining irrigation with air nanobubbles and low biochar supplementation did the translocation of the metals from soil to the aboveground tissues occur as the translocation factor was estimated to be greater than unity (TF > 1). The bioconcentration factors remained below 1.0 (BCF < 1) across all treatments, demonstrating limited mobilization from soil to plant tissues despite the application of soil amendments. Finally, the application of nanobubbles increased slightly but not substantially the total uptake of metals, which showed a significant decrease compared to the control groups when the lower dosage of biochar was utilized. Full article

Although the cultivation of food crops in farmland heavily contaminated by heavy metals is prohibited in China, vegetables can still be planted on a small-scale due to their short growth cycles and flexible sale models, posing a significant threat to local consumers. In this study, a pot culture experiment was conducted to investigate the feasibility of safe production through the in-situ stabilization of heavy metals in heavily contaminated soil. The remediation efficiency of wheat straw biochar and N-doped biochar, the growth of spinach, the heavy metal accumulation in spinach, and potential health risks were also explored. The results indicated that both biochar and N-doped biochar significantly affected the soil pH, cation exchange capacity, organic matter, available phosphorus, available potassium, alkaline nitrogen content, and spinach biomass, but the trends were variable. Additionally, the diethylenetriaminepentaacetic-extractable Pb, Cd, Cu, Zn, and Ni concentrations decreased 9.23%, 7.54%, 5.95, 7.44%, and 16.33% with biochar, and 10.46%, 12.91%, 21.98%, 12.62%, and 12.24% with N-doped biochar, respectively. Furthermore, N-doped biochar significantly reduced the accumulation of Pb, Cd, and Ni in spinach by 35.50%, 33.25%, and 30.31%, respectively. Health risk assessment revealed that the non-carcinogenic risk index for adults and children decreased from 17.0 and 54.8 to 16.3 and 52.5 with biochar and 11.8 and 38.2 with N-doped biochar, respectively, but remained significantly higher than the acceptable range (1.0). The carcinogenic risk assessment revealed that the risk posed by Cd in spinach exceeded the acceptable value (10⁻⁴) for both adults and children across all treatments. These results may imply that biochar and N-doped biochar cannot achieve the safe production of vegetables in soil heavily contaminated by heavy metals through in-situ stabilization. Full article

Odor emission has become a major issue in waste transfer stations. Hydrogen sulfide, methyl mercaptan (MM), and dimethyl disulfide (DMDS) are the main odorous gases. They have a low odor threshold and are difficult to remove. In this study, pine bark biochar was produced and modified with metal ions, including Ni²⁺, Ti²⁺, Mn²⁺, Zn²⁺, Mg²⁺, and Cu²⁺. It was then used for the removal of hydrogen sulfide, methyl mercaptan, and dimethyl disulfide. Among all modifications, the Cu²⁺ modified biochar showed the best sorption capacity, and the maximum sorption amounts were 20.50 mg/g for H₂S, 36.50 mg/g for MM, and 57.98 mg/g for DMDS. To understand the adsorption, BET, SEM, and XPS of the original and modified biochar were performed. This illustrated that modification with Cu²⁺ increased the surface area and porosity, thus enhancing the adsorption capacity. In the alkaline absorption study, it was found that the removal of the three odor gases increased with the pH increase. Based on the results, a combined process called absorption–adsorption was established to treat the odor gas generated in a local waste transfer station. Thirty-one gas components were detected in the odor gas of the waste transfer station. The process proceeded for 30 days, and these gas components were not found in the effluent during treatment. Regarding H₂S, MM, and DMDS, they were not detected even after 90 days. This indicates the high adsorption capacity of the modified biochar toward the three odor gases. In addition, the process is simple and easy to operate. This suggests that it is suitable for treating odor in places where there is no technician, and the odor needs efficient treatment. The study provides a feasible alternative for domestic waste transfer stations to control the odor problem. Full article

The issue of soil contamination by heavy metals (HMs) has attracted extensive attention. In the present study, the effects of four remediation measures combined with rice intercropping on the quality of soils were evaluated in a mildly HM-contaminated paddy field. The results showed that better comprehensive remediation effects were found in the intercropping system with high and low Cd-tolerant rice than in the monoculture system. Both foliar spraying of sodium selenite and inoculation with Pseudomonas TCd-1 significantly reduced the Nemerow comprehensive pollution index (NCPI) of the soils. The application of biochar and lime significantly increased the soil fertility index. Among all the treatments, the application of 30 t∙hm⁻² biochar and 3600 kg∙hm⁻² lime improved soil fertility the most. The lowest single-factor pollution indices (SFPIs) of Cd, Cu, Zn, Ni and Pb and the NCPI of the soils were observed in the treatment with foliar spraying of sodium selenite at 45 mg∙L⁻¹, showing the greatest comprehensive reduction in soil HMs. The application of 1200 kg∙hm⁻² lime and 30 t∙hm⁻² biochar and foliar spraying of 45 mg∙L⁻¹ sodium selenite effectively improved the soil quality. Overall, the soil quality of paddy fields dramatically influenced the cleaner production of rice and is of great significance to the maintenance of food security. Full article

Composite materials based on diatomite (DT) with the addition of biochar (BC), dolomite (DL), and bentonite (BN) were developed. The effect of chemical modification on the chemical structure of the resulting composites was investigated, and their influence on heavy metal immobilization and the ecotoxicity of post-flotation sediments was evaluated. It was demonstrated that the chemical modifications resulted in notable alterations to the chemical properties of the composites compared to pure DT and mixtures of DT with BC, DL, and BN. An increase in negative charge was observed in all variants. The addition of BC introduced valuable chemically and thermally resistant organic components into the composite. Among the chemical modifications, composites with the addition of perlite exhibited the lowest values of negative surface charge, which was attributed to the dissolution and transformation of silicon compounds and traces of kaolinite during their initial etching with sodium hydroxide. The materials exhibited varying efficiencies in metal immobilization, which is determined by both the type of DT additive and the type of chemical modification applied. The greatest efficacy in reducing the mobility of heavy metals was observed in the PFS with the addition of DT and BC without modification and with the addition of DT and BC after the modification of H₂SO₄ and H₂O₂: Cd 8% and 6%; Cr 71% and 69%; Cu 12% and 14%; Ni 10% and Zn 15%; and 4% and 5%. In addition, for Zn and Pb, good efficacy in reducing the content of mobile forms of these elements was observed for DT and DL without appropriate modification: 4% and 20%. The highest reduction in ecotoxicity was observed in the PFS with the addition of DT and BC, followed by BN and DL, which demonstrated comparable efficacy to materials with DT and BN. Full article

Nickel-based catalysts promoted by Mo-oxo species have been proven to be quite promising for transformation of triglycerides into green diesel. The selection of the support for such catalysts is crucial. In the present study, pyrolyzed rice husk subjected to acid and/or alkaline post-treatment was studied as support for the aforementioned catalysts. Biochar produced by slow pyrolysis of raw material at 850 °C for 5 h under limited-oxygen conditions exhibited the most promising textural characteristics. These were substantially improved by alkaline post-treatment. Thus, the corresponding MoNi catalysts proved the most efficient for upgrading used cooking oil (UCO) to green diesel via a solvent-free hydrotreatment process, performed in a semi-batch reactor (at 310 °C, 40 bar, 100 mL/min H₂, 100 mL UCO and 1 g of catalyst). The enhanced catalytic performance (complete conversion of UCO and 32 wt.% green diesel yield) of MoNi catalysts supported on biochar subjected at least to an alkaline post-treatment step has been attributed to their high SSA, suitable pore size distribution (enhanced mesoporosity), and acidity (enhanced population of acid sites with moderate strength), as well as to the high dispersion of the active phase. Full article