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Selective ring opening (SRO) catalysts transform polycyclic molecules in low grade oil to produce cleaner burning diesel fuel. Mechanistic insight, structure-reactivity relationships, catalyst design, and future opportunities for pyrolysis oil refining from municipal solid waste are discussed.

Perovskite oxides are regarded as promising electrocatalysts for water splitting due to their cost-effectiveness, high efficiency and durability in the oxygen evolution reaction (OER). Despite these advantages, a fundamental understanding of how critical structural parameters of perovskite electrocatalysts influence their activity and stability is lacking. Here, we investigate the impact of structural defects on OER performance for representative LaNiO3 perovskite electrocatalysts. Hydrogen reduction of 700¿°C calcined LaNiO3 induces a high density of surface oxygen vacancies, and confers significantly enhanced OER activity and stability compared to unreduced LaNiO3; the former exhibit a low onset overpotential of 380 mV at 10 mA¿cm-2 and a small Tafel slope of 70.8 mV¿dec-1. Oxygen vacancy formation is accompanied by mixed Ni2+/Ni3+ valence states, which quantum-chemical DFT calculations reveal modify the perovskite electronic structure. Further, it reveals that the formation of oxygen vacancies is thermodynamically more favourable on the surface than in the bulk; it increases the electronic conductivity of reduced LaNiO3 in accordance with the enhanced OER activity that is observed.

Global temperature has risen >1 °C since the preindustrial era, resulting in well-documented adverse climate impacts including extreme weather (floods, droughts, storms, and heat waves), a rise in ...

Recent research in catalyst development for CO2 methanation has been focussing on the design of nanostructures with high porosity and better redox properties. Herein, nanostructured Ce0.8Zr0.2O2 mixed oxide support was prepared by a metal organic framework (MOF)-template approach and its properties were well compared with a similar catalyst prepared by a conventional coprecipitation (CP) method. The MOF-template approach resulted in the production of a nanoporous Ce0.8Zr0.2O2 support with improved redox properties compared to the coprecipitated Ce0.8Zr0.2O2. The prepared support was then decorated with Co3O4 nanoparticles and tested in CO2 methanation reaction. At 320 °C, 1.5 MPa and GHSV = 15,000 mL g˗1 h˗1, the Co/Ce0.8Zr0.2O2 catalyst prepared by MOF-template method achieved far better CO2 conversion (81.2%) and improved CH4 selectivity (99%) than the catalyst prepared by CP method (48.7% CO2 conversion and 97% CH4 selectivity). The long-time presence of the MOF-derived Co/Ce0.8Zr0.2O2 catalyst on the stream proved its resistance towards sintering, which may be ascribed to the fine dispersion of Co3O4 nanoparticles as well as their excellent integration in the network of nanoporous Ce0.8Zr0.2O2.

Herein, the catalytic performance of Fe/Nb/M (M = Mn, Co, Ni, and Cu) spinel ferrites prepared by a co-precipitation method for the high-temperature water-gas shift (HT-WGS) was investigated. Incorporation of Nb into the iron oxide lattice was found to moderately improve the catalytic activity. Conversely, the co-doping with Nb and transition metals (Mn, Co, Ni, and Cu) into the iron oxide matrix drastically enhanced the HT-WGS activity. The high lattice strain/disorder and facile Fe3+/Fe2+ redox cycle induced by the enhanced synergism in the Fe/Nb/M ternary catalysts serve as active sites to efficiently catalyze the WGS reaction. The results also indicate that the Nb acts as a textural promoter to improve the thermal stability of the active magnetite phase, while the transition metals act as structural promoters to enhance the WGS activity. The Fe/Nb/Ni exhibited the higher catalytic performance among the co-doped spinel ferrite catalysts. The high lattice strain/disorder, facile reduction of hematite to magnetite and highly facilitated surface Fe3+/Fe2+ redox pair by strong synergistic effect could be responsible for the better activity and stability of Fe/Nb/Ni in HT-WGS reaction. The characterizations of the spent Fe/Nb/Ni after 100 h of reaction revealed that the catalyst exhibited an excellent structural and surface stability during the reaction.

The capacity of an adsorbent to bind and remove dye from solution greatly depends on the type of functionalization present on the nanoparticles surface, and its interaction with the dye molecules. Within this study, nitrogenous silane nanoparticles were hydrothermally synthesized resulting in the formation of rapid and highly efficient adsorbents for concentrated mixed dyes. The amorphous silane nanoparticles exhibited a monolayer based mechanism of mixed dye adsorption with removal capacities between 416.67 and 714.29 mg/g of adsorbent. Dye removal was predominantly due to the electrostatic attraction between the positively charged silane nanoparticles (13.22–8.20 mV) and the negatively charged dye molecules (−54.23 mV). Addition of H. annuus extract during synthesis resulted in three times the surface area and 10 times increased pore volume compared to the positive control. XPS analysis showed that silane treatments had various nitrogen containing functionalities at their surface responsible for binding dye. The weak colloidal stability of silane particles (13.22–8.20 mV) was disrupted following dye binding, resulting in their rapid coagulation and flocculation which facilitated the separation of bound dye molecules from solution. The suitability for environmental applications using these treatments was supported by a bacterial viability assay showing >90% cell viability in treated dye supernatants.

Perovskite oxides are regarded as promising electrocatalysts for water splitting due to their cost-effectiveness, high efficiency and durability in the oxygen evolution reaction (OER). Despite these advantages, a fundamental understanding of how critical structural parameters of perovskite electrocatalysts influence their activity and stability is lacking. Here, we investigate the impact of structural defects on OER performance for representative LaNiO

Design and synthesis of efficient photocatalyst systems for a large volume of hydrogen (H2) evolution under solar light is still a great challenge. To obtain high photocatalytic activity, graphene-based semiconductor photocatalysts are gaining heightened attention in the field of green and sustainable fuel production due to their good electronic properties, high surface area and chemical stability. Herein, we demonstrate an efficient, novel and smart architecture of a graphene-based ZnIn2S4/g-C3N4 nanojunction by a simple hydrothermal process for H2 generation. In the present study, graphene (G) is chosen as the electron mediator and ZnIn2S4 (ZIS) and g-C3N4 (CN) are chosen as two different semiconductor photocatalysts to construct a smart architecture for the ternary photocatalytic system. Different characterization techniques such as XRD, TGA, FT-IR, SEM, TEM, HR-TEM, XPS, BET, and UV-vis DRS were employed to ensure the successful integration of graphene, ZnIn2S4, and g-C3N4 in the nanocomposite. As a result, high and efficient H2 evolution (477 μmol h−1 g−1) is attained for the graphene-based ZnIn2S4/g-C3N4 nanocomposite. Transient photocurrent experiments, ESR, PL, and time-resolved PL studies suggested that the intimate ternary nanojunction effectively promotes fast charge transfer and thereby enhances photocatalytic H2 evolution.

Development of non-noble metal catalysts for oxidation of CO is an important subject for reducing the automotive emissions. Recently, shape-controlled synthesis of CeO2 has increasingly attracted the attention of researchers due to its size- and morphology-dependent unique properties. Following this line of thinking, herein, we successfully report the synthesis of Cr-doped CeO2 (Ce1−xCrxO2−δ; X = 0.05, 0.1, and 0.15) nanorods with various Cr contents by a facile hydrothermal method. Structural, surface, optical, and redox properties of the Cr-doped CeO2 nanorods were investigated by various techniques, namely, ICP-OES, TEM-HRTEM, FE-SEM/EDX/EDS, XRD, BET, Raman, UV–vis DRS, PL, XPS, H2-TPR, and O2-TPD. The catalytic performance was evaluated for CO oxidation. For comparison, the efficiency of Cr2O3 was also studied for CO oxidation under identical conditions. As revealed by various characterization results, the chromium ions were doped into the ceria lattice (formation of Ce–O–Cr solid solution), which enhanced the intrinsic properties such as oxygen vacancy concentration and surface area. It was found that the Cr-doped CeO2 nanorods show superior CO oxidation activity than the pristine counterparts (CeO2 nanorods and Cr2O3). The highest CO oxidation efficiency was achieved with the light-off temperature of T50 = 261 °C, when the Cr doping amount was 10% (Ce0.9Cr0.1O2−δ). A high specific surface area, more number of surface oxygen vacancies, a high concentration of Ce3+, and enhanced oxygen reducibility of Ce0.9Cr0.1O2−δ nanorods were found to be responsible for its superior catalytic performance. Further, the Ce0.9Cr0.1O2−δ nanorods exhibited a steady CO conversion over a period of 55 h investigated. The obtained results are expected to have a significant impact on the use of non-noble metal based Cr-doped CeO2 nanorods in environmental applications. The Cr-doped CeO2 nanorods with Ce0.9Cr0.1O2−δ composition showed enhanced CO oxidation performance at a lower temperature (~ 261 °C) than that of pristine CeO2 nanorods (338 °C) and Cr2O3 (361 °C) catalyst. This behaviour is a result of enhancement of oxygen vacancies, surface Ce3+ species, low-temperature reducibility, and high surface area.

The elemental mercury (Hg 0 ) vapor removal ability of α-MnO 2 nanotubes (NTs), nanorods (NRs) and nanowires (NWs) was evaluated in simulated natural gas mixtures. It was shown that NTs exhibited superior efficiency (~100%) at the temperature range of interest (25–100 °C). The Hg 0 breakthrough (corresponding to 99.5% Hg 0 removal efficiency) at ambient conditions and Hg 0 in = 870 μg∙m −3 , occurred after 48 h, reflecting a Hg 0 uptake of >10 mg∙g −1 (1 wt%). Most importantly, the developed nanosorbent was repeatedly, sufficiently regenerated at the relatively low temperature of 250 °C in a series of seven successive sorption-desorption tests, maintaining its capacity to remove all incoming Hg 0 in in each cycle. Interestingly, kinetic studies showed that at least 85% of total adhered Hg 0 could be recovered within the first hour of a 3-h regeneration process. Moreover, the presence of CO 2 and H 2 S did not affect its activity. The thermogravimetric analysis indicated significantly higher dehydration for NTs due to the loss of bound water inside its tunnels, likely indicating the presence of abundant surface adsorbed oxygen species which are believed to facilitate Hg 0 adsorption. This was also confirmed by X-ray spectroscopy, possibly explaining the enhanced activity of NTs.

Development of non-noble metal catalysts with improved structural, surface, and redox properties for catalytic soot oxidation has gained an enormous interest. Among practical alternatives, ceria-supported transition metal oxides have been proved to be the satisfactory catalysts for soot oxidation due to their outstanding redox properties and oxygen transfer capability promoted by the strong interaction between metal oxide and ceria interfaces. Following the above considerations, in the present work, CuO/Zn-CeO2 nanocomposite was prepared by a wet impregnation method and investigated for catalytic soot oxidation. To probe the significance of nanocomposites, pure counterparts, namely, CuO/CeO2, CuO/ZnO, and Zn-CeO2, were also synthesized. Various characterization techniques, namely, TEM-HRTEM, N2O chemisorption, XRD, ICP-OES, BET, Raman, XPS, and H2-TPR, were employed to investigate the structural, surface, and redox properties. Pure CuO/ZnO and CuO/CeO2 catalysts showed a soot oxidation activity with a T50 of 613 and 526 °C, respectively, under the practical conditions of NO concentration of 500 ppm and 20% O2. Interestingly, the CuO/Zn-CeO2 nanocomposite exhibited a remarkable higher soot oxidation activity with a T50 of 460 °C. The enhancement in the soot oxidation activity has been attributed to a strong interaction between the highly dispersed CuO and Zn-CeO2 support, which resulted in the desired textural properties and abundant surface defects (Ce3+ species as well as oxygen vacancies). In addition, the long-term stability test verifies an excellent reusability of the CuO/Zn-CeO2 nanocomposite towards soot oxidation without appreciable loss in the activity. The present study demonstrates the significance of ceria-based nanocomposite catalysts for environmental pollutant abatement.

In this study, we developed a novel method of integrating the well-accepted cold vapor technique with gold nanostructured based quartz crystal microbalance (QCM) devices to selectively detect mercury ions (Hg2+). This method allows for the conversion of aqueous mercury ions into elemental mercury (Hg°) vapor form and thereon use the highly sensitive QCM based mercury vapor sensors to detect the evolved mercury. The method involves reducing mercury chloride (HgCl2) in contaminated water by mixing it with a 2% tin chloride (SnCl2) solution in order to evolve Hg° vapor from the liquid mixture. The selectivity and sensitivity performance of each gold nanostructure, namely, the control Au thin film (Au-ctrl), Au-nanospheres (Au-NS) and Au-nanourchins (Au-NU), towards mercury vapor was evaluated. It was found that Au-NS and Au-NU sensors displayed up to 79% and 243% higher response magnitudes than the Au-ctrl sensor for various concentrations of HgCl2, respectively. All three sensors exhibited repeatable sensing performance when reporting the concentrations from 5 sensing events involving 500 ppb HgCl2 solution with Au-ctrl, Au-NS and Au-NU having the coefficient of variance (CoV) values of ˜5.7, 2.9 and 3.8%, respectively. Moreover, the sensors were observed to operate in the linear region with the mercury ion concentration range calibrated and tested. Importantly, the sensors showed no cross-interference effects when tested toward Hg2+ ions with and without the presence of other metal ions such as lead, cadmium, manganese, iron, and zinc. The results indicate that the CV-QCM technique developed is feasible to be potentially used in real-world mercury monitoring applications.

The sustainable synthesis of high-quality graphene sheets is one of the hottest and most inspiring topics in the fields of science and engineering. While the graphene oxide (GO) chemical reduction ...

Synergistic composite metal oxides are proven to be impressive materials due to their multi-functionalities across various catalytic applications. In a composite metal oxide, the interfacial chemistry between the components could provide exceptional redox and catalytic properties. In the present manuscript, the fundamental focus is devoted to investigating the interactions between active metal oxides at their interfaces and the catalytic activities towards diesel soot and CO oxidation. A series of flower-like microspheres namely, CeO2, 10%Mn3O4/CeO2, 20%Mn3O4/CeO2, and 40%Mn3O4/CeO2 catalysts were synthesized, where the effect of different Mn3O4 loadings towards soot combustion and CO oxidation were investigated. The characteristic 50% conversion temperature (T50) of catalytic soot oxidation under loose and tight contact conditions for CeO2 microspheres are 502 and 484 °C, respectively. After the integration of Mn3O4 and CeO2, the T50 values were decreased with the lowest values observed for the 20%Mn3O4/CeO2 microspheres (381 and 350 °C). Similarly, 20%Mn3O4/CeO2 microspheres showed T50 value at 103 °C for CO oxidation when compared to pure CeO2 microspheres (216 °C) and Mn3O4 nanoparticles (356 °C). Activation energy values were decreased when the Mn3O4/CeO2 composite used in soot and CO oxidation. The high catalytic activity can be attributed to the strong synergistic interactions between CeO2 and Mn3O4, variable oxidation states, the amount of readily available surface redox active sites and oxygen vacancies. The possible interfacial interaction between CeO2 and Mn3O4 can be exploited to exhibit enhanced surface structural, and redox properties when compared to the pure counterparts. Post-catalytic oxidation analysis confirms the high stability of the Mn3O4/CeO2 composite. The present study points out the vital role of interfacial interactions in composite metal oxides for improving the surface and redox properties, which are important for the development of highly efficient soot and CO oxidation catalysts.

TiO2 nanorods-supported MnOx, FeOx, CrOx, and MnOx-FeOx-CrOx catalysts have been prepared by a deposition-precipitation method, with the aim of investigating the combination of ternary metal oxides effect on elemental mercury (Hg0) removal. The TiO2 nanorods-supported MnOx-FeOx-CrOx catalyst manifested the superior Hg0 removal efficiency (∼80-83%) at low temperatures (100–200 °C) in the presence of O2. The addition of NO promoted the Hg0 removal efficiency under the same reaction conditions. Further, SEM, HRTEM, XRD, BET surface area, and XPS characterization were carried out to explore the physicochemical properties of the catalysts. It was found that the integration of three active metal oxides contributed to the enrichment of active sites and the surface adsorbed oxygen species, thereby improving the catalytic activity. Additionally, both the large surface area and high crystallization of the obtained TiO2 nanorods resulted in uniform dispersion of the manganese-iron-chromium mixed metal oxide nanoparticles and a high activity. Further, XPS data of spent MnOx-FeOx-CrOx/TiO2 catalyst indicated that the presence of Mn4+, Cr6+, and Fe3+ could promote Hg0 oxidation due to the strong synergistic interaction between the TiO2 nanorods-incorporated MnOx, FeOx, and CrOx nanoparticles.

Herein, we report a highly efficient nanoporous Cu/CeO2 catalyst from metal organic frameworks (MOFs) for low-temperature WGS reaction. The MOF template approach delivered Cu/CeO2 nanocatalysts with larger surface areas and higher Cu dispersion, resulting better redox behaviour compared to Cu/CeO2 which was synthesized by a conventional co-precipitation method. The MOF derived Cu/CeO2 catalyst showed excellent catalytic performance (>90% CO conversion) for the WGS reaction at low temperature. It also maintained a long-term stability of 90 h operation, after which the CO conversion was still greater than 80%. Our results present advances in the exploitation of MOF templated nanoporous catalysts not only for WGS reaction but also for other catalytic applications.

A demand for functionalization of novel materials and surfaces has accelerated the study of preparation methods for thin films and coatings. Preparation of catalytically active materials such as metal oxides, mixed oxides, zeolites and hydrotalcites in the form of thin films and coatings has led to chemical and physical properties widely different from those of their bulk analogues. Conventional applications of zeolite powders were limited to ion-exchange, sorption and catalysis. However, recent advances in synthesis methods for controlling the catalyst architecture in two and three dimensions have led to discovery of new applications for zeolitic materials. Zeolite thin films and coatings have experienced a high demand arising from their applications in monolith catalysts, catalytic membrane reactors, permeation barriers, anti-reflective surfaces, low dielectric constant materials and sensing. In addition, zeolite thin films have facilitated a better understanding of the relationship between their crystalline structure and functional activity. Such understanding has given a boost to rational design of functional materials for targeted applications. Latest developments in methods of thin film preparation demonstrate the preparation of well-ordered directionally oriented thin films and coatings. This review focuses on conventional and modern synthetic methods used for preparation of catalytically active thin films and coatings. It is evident from the tremendous growth and improvements observed in this research area that catalyst coatings and micro channel reactors will play a very important role in industrial catalysis as well as academic research in the imminent future.

Catalytic hydrogenation of 1,3-butadiene to produce selectively 1-butene has considerable importance in the hydrocarbon industry and presents a significant challenge in tuning the catalyst selectivity towards 1-butene, understanding the reaction and kinetic mechanism. Selective hydrogenation over metal oxide-supported palladium catalysts is considered as a standard process; however, selectivity towards 1-butene is achieved by alloying palladium with other metals that facilitate the desorption of adsorbed alkene intermediate and limit further hydrogenation to form butane. In this book chapter, we summarize the current state of the art and perception of various factors that control the catalyst activity, adsorption of intermediates on the active sites and eventually the selectivity. In particular, we present a concise description of active metal dispersion, structure sensitivity, influence of support, promoter and their role in governing the selectivity of 1-butene from 1,3-butadiene hydrogenation. Then, this chapter highlights the detailed analysis of reaction kinetics and reaction mechanisms that are proposed clearly. Finally, a brief overview of the theoretical investigations for 1,3-butadiene hydrogenation using density functional theory (DFT) calculations has also been discussed for a variety of catalysts and followed discussion about summary and future outlook.

Complex organic molecules are of great importance to research and industrial chemistry and typically synthesized from smaller building blocks by multistep reactions. The ability to perform multiple (distinct) transformations in a single reactor would greatly reduce the number of manipulations required for chemical manufacturing, and hence the development of multifunctional catalysts for such one-pot reactions is highly desirable. Here we report the synthesis of a hierarchically porous framework, in which the macropores are selectively functionalized with a sulfated zirconia solid acid coating, while the mesopores are selectively functionalized with MgO solid base nanoparticles. Active site compartmentalization and substrate channelling protects base-catalysed triacylglyceride transesterification from poisoning by free fatty acid impurities (even at 50 mol%), and promotes the efficient two-step cascade deacetalization-Knoevenagel condensation of dimethyl acetals to cyanoates.

The construction of highly efficient inorganic mimetic enzymes (nanozymes) is much needed to replace natural enzymes due to their instability and high cost. Recently, nanoscale CeO

In recent years, the development of artificial nanostructured enzymes has received enormous interest in nanobiotechnology due to their advantages over natural enzymes. In the present work, different amounts (5, 10, and 20 wt%) of Co

We report an enhancement in the efficiency of agitative liquid-phase exfoliation of stratified WS2 crystals under the influence of an electric field. We have been successfully able to increase the exfoliation efficiency of WS2 nanoflakes using a co-applied alternating electric field. Loss of centrosymmetry at the facial layers of WS2, together with the matching between the dispersive component of this material and solvent that weakens the van der Waals forces, augment the exfoliation process. However, this is not seen for MoS2 and graphene. The outcomes provide the base for future investigations on the influence of electric field for the exfoliation of layered structures.

Oxygen vacancies in inorganic semiconductors play an important role in reducing electron–hole recombination, which may have important implications in photocatalysis. Cuprous oxide (Cu2O), a visible light active p-type semiconductor, is a promising photocatalyst. However, the synthesis of photostable Cu2O enriched with oxygen defects remains a challenge. We report a simple method for the gram-scale synthesis of highly photostable Cu2O nanoparticles by the hydrolysis of a Cu(I)-triethylamine [Cu(I)–TEA] complex at low temperature. The oxygen vacancies in these Cu2O nanoparticles led to a significant increase in the lifetimes of photogenerated charge carriers upon excitation with visible light. This, in combination with a suitable energy band structure, allowed Cu2O nanoparticles to exhibit outstanding photoactivity in visible light through the generation of electron-mediated hydroxyl (OH˙) radicals. This study highlights the significance of oxygen defects in enhancing the photocatalytic performance of promising semiconductor photocatalysts.

In this work, various transition and rare earth metal ions (M3+; M = Mn3+, Fe3+, La3+, and Pr3+) doped CeO2 solid solutions were prepared by a simple sol–gel method for the degradation of an organic dye, Rhodamine B (RhB) as a model pollutant. The as-prepared samples were thoroughly studied by various characterization techniques to understand the surface and optical properties. The XRD results suggested formation of solid solutions, and TEM studies confirmed the nanosized nature of the ceria particles. The Raman and XPS results revealed that the doping of metal ions enhanced the formation of Ce3+ ions associated with the oxygen vacancies. The doping of M3+ ions in the CeO2 lattice strongly influenced the band gap tuning of undoped CeO2 (3.01 eV) from the UV to Visible region (i.e., 2.45–2.90 eV). Photoluminescence studies suggested that doping of M3+ cations suppresses the recombination rate of photogenerated electron–hole pairs. The photocatalytic activity results indicated that the doped CeO2 samples exhibit substantially enhanced photocatalytic performance for the degradation of RhB compared to undoped CeO2. The better catalytic activity of doped CeO2 samples could be attributed to the presence of defects (Ce3+ ions and oxygen vacancies), which play a prominent role as trapping centres for excited electrons and inhibit the recombination process. The scavengers tests confirmed that the generation of highly reactive hydroxyl (·OH) and super oxide (·O2−) radicals are actively involved in the photodegradation process. This work rendered a new concept for rational design and development of doped CeO2-based materials as better photocatalysts.

In the present work, nanowire morphologies of α-MnO2, cobalt monodoped α-MnO2, Cu and Co bidoped α-MnO2, and Ni and Co bidoped α-MnO2 samples were prepared by a facile hydrothermal synthesis. The structural, morphological, surface, and redox properties of all the as-prepared samples were investigated by various characterization techniques, namely, scanning electron microscopy (SEM), transmission and high resolution electron microscopy (TEM and HR-TEM), powder X-ray diffraction (XRD), N2 sorption surface area measurements, X-ray photoelectron spectroscopy (XPS), hydrogen-temperature-programmed reduction (H2-TPR), and oxygen-temperature-programmed desorption (O2-TPD). The soot oxidation performance was found to be significantly improved via metal mono- and bidoping. In particular, Cu and Co bidoped α-MnO2 nanowires showed a remarkable improvement in soot oxidation performance, with its T50 (50% soot conversion) values of 279 and 431 °C under tight and loose contact conditions, respectively. The soot combust...

A novel one-step microwave irradiation method has been introduced to synthesize 3-mercaptopropionic acid capped CdTe QDs (Quantum dots). The synthesis process required no special conditions such as an inert nitrogen atmosphere but was carried out using TeO 2 (Tellurium oxide) as opposed to the Te powder, Na 2 TeO 3 or Al 2 TeO 3 usually used for the tellurium source. The characterization of the QDs revealed that they were 2–3 nm in size. The application of aqueous synthesis of capped CdTe QDs for latent fingerprinting was explored and fast turnaround times were achieved.

In recent years, the development of artificial nanostructured enzymes has received enormous interest in nanobiotechnology due to their advantages over natural enzymes. In the present work, different amounts (5, 10, and 20 wt%) of Co3O4 nanoparticle decorated CeO2 hybrid flower-like microspheres (Co3O4@CeO2) have been investigated for peroxidase-like activity and it was found that 10 wt% of Co3O4@CeO2 exhibited excellent peroxidase-like activity for the catalytic oxidation of the 3,3′,5,5′-tetramethylbenzidine (TMB) substrate in the presence of H2O2. The formation of more Ce3+ ions associated with the oxygen vacancies and a strong synergistic interaction between CeO2 and Co3O4 may be responsible for the enhanced peroxidase-like activity. Based on their peroxidase activity, Co3O4@CeO2 hybrid microspheres were used for the colourimetric detection of glucose. It was found that Co3O4@CeO2 hybrid microspheres showed a substantial enhancement in the detection selectivity. The limit of detection (LOD) was also improved with a limit as low as 1.9 μM. Thus, we believe that Co3O4@CeO2 hybrid flower-like microspheres with high peroxidase-like activity can be exploited for biosensing applications.

Design and synthesis of efficient photocatalyst systems for a large volume of hydrogen (H

CeO2 nanoparticle-decorated ?-MnO2 nanotubes (NTs) were prepared and tested for elemental mercury (Hg0) vapor removal in simulated natural gas mixtures at ambient conditions. The composition which ...

CeO

In this investigation, Mn-doped CeO2(CM) catalysts were prepared by co-precipitation (CP), sol-gel (SG), and hydrothermal (HT) methods and characterized by XRD, ICP-OES, N2 adsorption–desorption, SEM, TEM-HREM, Raman, XPS, FT-IR, XPS and H2-TPR techniques, and evaluated for CO oxidation activity. The CM catalyst obtained by HT method showed superior CO oxidation performance at much lower temperature (T50 = ~355 K). The better performance of CM-HT catalyst is ascribed to its larger surface area, higher concentration of surface adsorbed oxygen, enhanced reducibility, and more oxygen vacancy sites. Further, it was found that the CM-HT catalyst is fully recyclable for over four runs while maintaining its high activity, which suggests that it is a better catalyst for CO oxidation at lower temperatures.

The construction of highly efficient inorganic mimetic enzymes (nanozymes) is much needed to replace natural enzymes due to their instability and high cost. Recently, nanoscale CeO2 has been attracting significant interest due to its unique properties such as facile redox behaviour (Ce4+ ↔ Ce3+) and surface defects. In the present work, various amounts of Fe3+-doped CeO2 nanorods (NRs) (with 3, 6, 9, and 12% Fe doping) were synthesized using a facile hydrothermal method and investigated for peroxidase-like activity and glucose detection. The peroxidase-like activity results revealed that 6 at% doping is the optimal Fe doping level to demonstrate superior catalytic performance over un-doped and Fe3+-doped CeO2 NRs. Steady state kinetic analysis also confirms that the 6% Fe3+-doped CeO2 (6Fe/CeO2) NRs exhibited excellent catalytic performance towards 3,3′,5,5′tetramethylbenzidine (TMB) oxidation with a Km and Vm of 0.176 mM and 8.6 × 10−8 M s−1, respectively, as compared to horseradish peroxidase (HRP) enzymes (0.434 mM and 10.0 × 10−8 M s−1). Typical colour reactions arising from the catalytic oxidation of the TMB substrate over 6Fe/CeO2 NRs with H2O2 have been utilized to establish a simple sensitive and selective colorimetric assay for the determination of glucose concentration in buffer, diluted fruit juices and foetal bovine serum samples. The superior catalytic performance of 6Fe/CeO2 NRs could be attributed to abundant surface defects, high surface area and pore volume, and preferential exposure of the highly reactive (110) planes.

Surface active sites such as oxygen vacancies, Ce3+ ions, and unsaturated coordinated sites on nano ceria (CeO2) are significant in catalytic oxidation reactions. The recent development in nanoengineered CeO2 made a pathway to extend its use in various catalytic applications. In this study, transition metals (Mn2+, Ni2+, and Co2+) doped CeO2 nanorods (NRs) were prepared by hydrothermal method and tested towards CO oxidation. Furthermore, the samples were characterized by various physicochemical techniques, namely, TEM and HR-TEM, SEM-EDX, XRD, ICP-OES, BET surface area, Raman spectroscopy, XPS, and H2-TPR. The results demonstrated that the incorporation of dopants greatly enhances the surface defective sites (Ce3+ ions and a high degree of surface roughness) and redox properties of CeO2 NRs and thereby improved catalytic activity. Especially, the Co–CeO2 NR catalyst exhibited better CO conversion (T50 ∼ 145 °C) when compared to pure CeO2 NR (T50 ∼ 312 °C).

A series of MnOx/CeO2 (Mn/Ce), MnOx/ZrO2 (Mn/Zr), and MnOx/Ce0.75Zr0.25O2 (Mn/CZ) catalysts prepared by an impregnation method were tested for their ability to catalyse the oxidation of Hg0 at relatively low temperature (423 K). Various characterization techniques, namely, Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR) were employed to understand the structural, surface, and redox properties of the prepared catalysts. Specific aspects of the catalysis of Hg0 oxidation that were investigated included the influence of MnOx loading (5, 15, and 25%) and the influence of HCl and O2. Among the catalysts tested, the 15Mn/CZ catalyst achieved the best Hg0 oxidation performance (~83% conversion of Hg0 to Hg2+) in the presence of HCl and O2. The higher activity of the 15Mn/CZ catalyst was most likely due to the presence of more oxygen vacancies, enhanced Mn4+/Mn4+ + Mn3+ + Mn2+ ratio and more surface adsorbed oxygen, which were proved by XRD, BET, Raman, and XPS. H2-TPR results also show that the strong interaction between the Ce0.75Zr0.25O2 support and MnOx improved the redox properties significantly as compared to pure CeO2 and ZrO2 supported MnOx catalysts.

Due to the lenient environmental policies in developing economies, mercury-containing wastes are partly produced as a result of the employment of mercury in manufacturing and consumer products. Worldwide, the presence of mercury as an impurity in several industrial processes leads to significant amounts of contaminated waste. The Minamata Convention on Mercury dictates that mercury-containing wastes should be handled in an environmentally sound way according to the Basel Convention Technical Guidelines. Nevertheless, the management policies differ a great deal from one country to another because only a few deploy or can afford to deploy the required technology and facilities. In general, elemental mercury and mercury-bearing wastes should be stabilized and solidified before they are disposed of or permanently stored in specially engineered landfills and facilities, respectively. Prior to physicochemical treatment and depending on mercury's concentration, the contaminated waste may be thermally or chemically processed to reduce mercury's content to an acceptable level. The suitability of the treated waste for final disposal is then assessed by the application of standard leaching tests whose capacity to evaluate its long-term behavior is rather questionable. This review critically discusses the main methods employed for the recovery of mercury and the treatment of contaminated waste by analyzing representative examples from the industry. Furthermore, it gives a complete overview of all relevant issues by presenting the sources of mercury-bearing wastes, explaining the problems associated with the operation of conventional discharging facilities and providing an insight of the disposal policies adopted in selected geographical regions.

The role of natural gas in mitigating greenhouse gas emissions and advancing renewable energy resource integration is undoubtedly critical. With the progress of hydrocarbons exploration and production, the target zones become deeper and the possibility of mercury contamination increases. This impacts on the industry from health and safety risks, due to corrosion and contamination of equipment, to catalyst poisoning and toxicity through emissions to the environment. Especially mercury embrittlement, being a significant problem in LNG plants using aluminum cryogenic heat exchangers, has led to catastrophic plant incidents worldwide. The aim of this review is to critically discuss the conventional and alternative materials as well as the processes employed for mercury removal during gas processing. Moreover, comments on studies examining the geological occurrence of mercury species are included, the latest developments regarding the detection, sampling and measurement are presented and updated information with respect to mercury speciation and solubility is displayed. Clean up and passivation techniques as well as disposal methods for mercury-containing waste are also explained. Most importantly, the environmental as well as the health and safety implications are addressed, and areas that require further research are pinpointed.

The necessity to drastically act against mercury pollution has been emphatically addressed by the United Nations. Coal-fired power plants contribute a great deal to the anthropogenic emissions; therefore, numerous sorbents/catalysts have been developed to remove elemental mercury (Hg0 ) from flue gases. Among them, ceria (CeO2 ) has attracted significant interest, due to its reversible Ce3+ /Ce4+ redox pair, surface-bound defects and acid-base properties. The removal efficiency of Hg0 vapor depends among others, on the flue gas composition and temperature. CeO2 can be incorporated into known materials in such a way that the abatement process can be effective at different operating conditions. Hence, the scope of this account is to discuss the role of CeO2 as a promoter, active phase and support in the design of composite Hg0 sorbents/catalysts. The elucidation of each of these roles would allow the integration of CeO2 advantageous characteristics to such degree, that tailor-made environmental solution to complex issues can be provided within a broader application scope. Besides, it would offer invaluable input to theoretical calculations that could enable the materials screening and engineering at a low cost and with high accuracy.

Oxygen vacancies in inorganic semiconductors play an important role in reducing electron-hole recombination, which may have important implications in photocatalysis. Cuprous oxide (Cu2O), a visible light active p-type semiconductor, is a promising photocatalyst. However, the synthesis of photostable Cu2O enriched with oxygen defects remains a challenge. We report a simple method for the gram-scale synthesis of highly photostable Cu2O nanoparticles by the hydrolysis of a Cu(i)-triethylamine [Cu(i)-TEA] complex at low temperature. The oxygen vacancies in these Cu2O nanoparticles led to a significant increase in the lifetimes of photogenerated charge carriers upon excitation with visible light. This, in combination with a suitable energy band structure, allowed Cu2O nanoparticles to exhibit outstanding photoactivity in visible light through the generation of electron-mediated hydroxyl (OH˙) radicals. This study highlights the significance of oxygen defects in enhancing the photocatalytic performance of promising semiconductor photocatalysts.

This work presents the synthesis and characterization of alumina supported ceria–manganese solid solutions (Ce–Mn/Al), which were prepared by a deposition coprecipitation method followed by calcination at different temperatures from 773 to 1073 K. The physicochemical properties of the synthesized samples were deeply investigated by various characterization techniques, namely, XRD, ICP-OES, BET surface area, TEM-HRTEM, Raman, XPS, and H2-TPR. The catalytic activity was evaluated for CO oxidation. BET surface area measurements revealed that synthesized samples exhibit reasonably high specific surface area. XRD and Raman results confirmed that the present Ce–Mn/Al samples are single-phase solid solutions with good structural homogeneity and high thermal stability up to 1073 K. TEM analyses showed that the particle sizes of Ce–Mn/Al samples are in the range of ∼5–14 nm. XPS analysis revealed that Ce is in the form of Ce4+ and Ce3+, and Mn existed in the form of Mn4+, Mn3+, and Mn2+ on the surface of the samples. The solid solution particles in the nanosize form are well distributed over the support surface. As a result of solid solution formation and high dispersion over the support, the Ce–Mn/Al samples exhibited better redox behaviour. The CO oxidation results revealed that the Ce–Mn/Al samples show an excellent CO oxidation performance compared with alumina supported undoped CeO2 (Ce/Al) and MnOx (Mn/Al) samples. Among various samples, the Ce–Mn/Al calcined at 773 K showed outstanding CO activity with T50 = ∼340 K. The enhanced catalytic activity was mainly attributed to high surface area, large amount of oxygen vacancies, and excellent redox behaviour. The metal–support interaction also seems to play a decisive role in their high catalytic activity by stabilizing the Ce–Mn–O dispersion.

In this work, nanosized Ce0.7M0.3O2−δ (M = Mn, Fe, Co) solid solutions were prepared by a facile coprecipitation method and evaluated for CO oxidation. The physicochemical properties of the synthesized samples were investigated by various characterization techniques, namely, XRD, ICP-OES, BET surface area, SEM-EDX, TEM and HRTEM, Raman, XPS, and H2-TPR. XRD studies confirmed the formation of nanocrystalline single phase Ce0.7M0.3O2−δ solid solutions. ICP-OES analysis confirmed actual amount of metal loadings in the respective catalysts. The BET surface area of Ce0.7M0.3O2−δ samples significantly enhanced after the incorporation of dopants. TEM studies confirmed nanosized nature of the samples and the average particle sizes of Ce0.7M0.3O2−δ were found to be in the range of ∼8–16 nm. Raman studies indicated that the incorporation of dopant ions into the CeO2 lattice promote the formation of more oxygen vacancies. The existence of oxygen vacancies and different oxidation states (Ce3+/Ce4+ and Mn2+/Mn3+, Fe2+/ Fe3+, and Co2+/Co3+) in the doped CeO2 samples were further confirmed from XPS investigation. TPR measurements revealed an enhanced reducibility of ceria after the incorporation of dopants. The catalytic activity results indicated that the doped CeO2 samples show excellent CO oxidation activity and the order of activity was found to be Ce0.7Mn0.3O2−δ > Ce0.7Fe0.3O2−δ > Ce0.7Co0.3O2−δ > CeO2. The superior CO oxidation performance of CeO2-MnOx has been attributed to a unique Ce-Mn synergistic interaction, which facilitates materials with promoted redox properties and improved oxidation activity.

Nanosized CeO2-MnOx mixed oxides with different Ce/Mn ratios were prepared by a citric acid-assisted sol-gel method. The effect of the MnOx content on structural, redox, and surface properties of the CeO2-MnOx was investigated by various techniques, namely, BET surface area, SEM, XRD, ICP-OES, Raman and FT-IR spectroscopy, H2-TPR, and XPS. Catalytic activity was evaluated with soot-catalyst mixture under tight contact conditions. BET surface area analysis indicated that Mn doping favors an enhancement in the surface area of pure CeO2. Raman active peaks for both pure CeO2 and CeO2-MnOx mixed oxides were determined at ca. 460 cm-1. The observed Raman shift can also be assigned to Raman active modes of CeO2 that are shifted from the original position due to different Mn doping. Formation of Ce1-xMnxO2-δ solid solutions was further confirmed by XRD and FT-IR analysis. H2-TPR results demonstrate that Ce1-xMnxO2-δ solid solutions significantly improved the redox property over the pure CeO2 or MnOx. XPS analysis reveal that Ce is in the form of Ce4+ and Ce3+, and Mn existed in the form of Mn4+, Mn3+, and Mn2+ on the surface of the samples. Catalytic activity results indicate that the oxidation temperature of soot can be significantly reduced by CeO2-MnOx mixed oxides, which render higher Ce3+ concentration and more surface oxygen vacancies compared with pure CeO2. Particularly, the Ce0.7Mn0.3O2-δ sample exhibited highest activity (a shift of T50 by ca. 122 K) compared to pure ceria.