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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.

In hydrogen processes, managing CO emissions and removal by catalytic oxidation is crucial during H2 production, storage/transportation, and use, ensuring the efficiency and safety of hydrogen systems and contributing to more sustainable energy solutions. Perovskite-structured transition metal oxide catalysts have been widely studied in various energy and environmental applications due to their extensive compositional modifications and electronic adjustments, facilitating catalytic behavior. Here, Ce-based perovskite catalysts with dual active metal doping at varying Co and Ni ratios are investigated to understand their structural and redox properties in CO oxidation. The reaction mechanism involves CO adsorption, oxygen activation, and redox cycling, confirming catalytic turnover. In situ DRIFTS analysis reveals real-time surface transformations with catalytic activity, which vary with Co and Ni doping ratio. Relatively, CO adsorption on Co3+ dominates the low-temperature activity, whereas Ni contributes to the efficiency at elevated temperatures. LCCNTxy (La0.7Ce0.1CoxNiyTi0.6O3) with x = 0.3 and y = 0.1 exhibits the highest performance, achieving T10 above 40 °C and the fastest T90 at 230 °C. This study highlights the compositional tuning in dual-doped perovskites and complementary roles of Co and Ni in CO oxidation for developing efficient industrial catalysts.

Hydrogen is mainly produced by steam reforming of fossil fuels. Thus, research has been continuously conducted to produce hydrogen by replacing fossil fuels. Among various alternative resources, waste is attracting attention as it can produce hydrogen while reducing the amount of landfill and incineration. In order to produce hydrogen from waste, the water–gas shift reaction is one of the essential processes. However, syngas obtained by gasifying waste has a higher CO concentration than syngas produced by steam reforming of fossil fuels, and therefore, it is essential to develop a suitable catalyst. Research on developing a catalyst for producing hydrogen from waste has been conducted for the past decade. This study introduces various catalysts developed and provides basic knowledge necessary for the rational design of catalysts for producing hydrogen from waste-derived syngas.

This study investigated the optimization of the remanufacturing process for spent Ni–Mo/γ-Al2O3 catalysts utilized in hydrodesulfurization (HDS) reactions. The proposed process encompasses essential steps, including oil washing, partial incineration, acid leaching, and complete incineration, aimed at restoring the physicochemical properties of the spent catalysts. The incorporation of partial incineration enhanced the removal of hydrocarbons and sulfur compounds, leading to notable recovery of surface area and pore volume. However, vanadium removal was insufficient with partial incineration alone, necessitating the use of an optimized acid-leaching step, where the leaching time was adjusted. The remanufactured catalysts demonstrated superior performance in HDS reactions compared to their fresh counterparts. The OPA(60)C catalyst, remanufactured through oil washing, partial incineration, 60 min of acid leaching, and complete incineration, exhibited the highest desulfurization efficiency. These findings highlight the critical role of impurity removal and the optimization of the acid-leaching duration in restoring catalyst activity. By enabling effective catalyst reuse, this process offers a sustainable and cost-effective solution for industrial applications.

Research is being actively conducted to improve the carbon deposition and sintering resistance of Ni-based catalysts. Among them, the Al2O3-supported Ni catalyst has been broadly studied for the dry reforming reaction due to its high CH4 activity at the beginning of the reaction. However, there is a problem of deactivation due to carbon deposition of Ni/Al2O3 catalyst and sintering of Ni, which is a catalytically active material. Supplementing MgO in Ni/Al2O3 catalyst can result in an improved MgAl2O4 spinel structure and basicity, which can be helpful for the activation of methane and carbon dioxide molecules. In order to confirm the optimal supports’ ratio in Ni/MgO-Al2O3 catalysts, the catalysts were prepared by supporting Ni after controlling the MgO:Al2O3 ratio stepwise, and the prepared catalysts were used for CO2 reforming of CH4 (CDR) using coke oven gas (COG). The catalytic reaction was conducted at 800 °C and at a high gas hourly space velocity (GHSV = 1,500,000 h−1) to screen the catalytic performance. The Ni/MgO-Al2O3 (MgO:Al2O3 = 3:7) catalyst showed the best catalytic performance between prepared catalysts. From this study, the ratio of MgO:Al2O3 was confirmed to affect not only the basicity of the catalyst but also the dispersion of the catalyst and the reducing property of the catalyst surface.

To develop customized sulfur–resistant catalysts for the water gas shift (WGS) reaction in the waste–to–hydrogen process, the effects of changing the nucleation conditions of the CeO2 support on catalytic performance were investigated. Supersaturation is a critical kinetic parameter for nuclei formation. The degree of supersaturation of the CeO2 precipitation solution was controlled by varying the cerium precursor concentration from 0.02 to 0.20 M. Next, 2 wt.% of Pt was impregnated on those various CeO2 supports by the incipient wetness impregnation method. The prepared samples were then evaluated in a WGS reaction using waste–derived synthesis gas containing 500 ppm H2S. The Pt catalyst supported by CeO2 prepared at the highest precursor concentration of 0.20 M exhibited the best sulfur resistance and catalytic activity regeneration. The sulfur tolerance of the catalyst demonstrated a close correlation with its oxygen storage capacity and easier reducibility. The formation of oxygen vacancies in CeO2 supports is promoted by the formation of small crystals due to a high degree of supersaturation.

Rh/CeO2–ZrO2 catalysts with various CeO2/ZrO2 ratios have been applied to H2 production from ethanol steam reforming at low temperatures. The catalysts all deactivated with time on stream (TOS) at 350 °C. The addition of 0.5% K has a beneficial effect on catalyst stability, while 5% K has a negative effect on catalytic activity. The catalyst could be regenerated considerably even at ambient temperature and could recover its initial activity after regeneration above 200 °C with 1% O2. The results are most consistent with catalyst deactivation due to carbonaceous deposition on the catalyst.

Residue hydrodesulfurization (RHDS) is a critical process in the petroleum refining industry for removing sulfur compounds from heavy residual oils. However, catalysts used in RHDS can easily be deactivated by numerous factors, leading to reduced process efficiency and economic benefits. The remanufacturing of spent catalysts can be a useful strategy for extending the lifespan of catalysts, reducing waste, and improving process sustainability. This paper proposes an effective catalyst remanufacturing process for commercial RHDS catalysts. In detail, sequential unit processes including oil washing (OW), complete incineration (CI), and acid leaching (AL) were conducted to remanufacture the spent RHDS catalysts. We also highlight some of the key challenges in remanufacturing catalysts, such as the key factors involved in catalyst deactivation. Finally, we provide future perspectives on the development of an effective catalyst remanufacturing process for RHDS, with the goal of improving the efficiency, sustainability, and competitiveness of the petroleum refining industry.

To improve the sulfur tolerance of CeO2-supported Pt catalysts for water gas shift (WGS) using waste-derived synthesis gas, we investigated the effect of synthesis methods on the physicochemical properties of the catalysts. The Pt catalysts using CeO2 as a support were synthesized in various pathways (i.e., incipient wetness impregnation, sol-gel, hydrothermal, and co-precipitation methods). The prepared samples were then evaluated in the WGS reaction with 500 ppm H2S. Among the prepared catalysts, the Pt-based catalyst prepared by incipient wetness impregnation showed the highest catalytic activity and sulfur tolerance due to the standout factors such as a high oxygen-storage capacity and active metal dispersion. The active metal dispersion and oxygen-storage capacity of the catalyst showed a correlation with the catalytic performance and the sulfur tolerance.

Simulated waste-derived synthesis gas has been tested for hydrogen production through water gas shift (WGS) reaction in the temperature range of 350–550 °C over chromium free Fe/Al/Cu oxide based catalysts. The CuO loading amount was optimized to get highly active Fe/Al/Cu oxide based catalysts for the high temperature WGS. Despite the high CO content in the feed gas (38.2 % dry basis), 15 % CuO catalyst exhibited the highest CO conversion (86 %) and 100 % selectivity to CO 2 at a very high gas hourly space velocity (GHSV) of 40,057 h −1 due to easier reducibility, the synergy effect of copper and aluminum, and the stability of the active phase (magnetite: Fe 3 O 4 ). Graphical Abstract