Insights into the Influence of ZrO2 Crystal Structures on Methyl Laurate Hydrogenation over Co/ZrO2 Catalysts

Core-shell Ni/SiO2@ZrO2 catalyst for highly selective CO2 conversion accompanied by enhancing reaction stability

CO2 RWGS reaction was considered to be a promising process for carbon dioxide conversion, however it retained a big challenge owing to methanation and metal sintering. Therefore, it was desperately needed to devise highly selective and stable catalyst. Herein, core-shell Ni/SiO2@ZrO2 catalyst was successfully prepared via a combination of the wet impregnation and in-situ hydrothermal synthesis method, with ZrO2 as the coating shell. The optimized Ni/SiO2@4ZrO2 catalyst possessed enhanced metal-support interaction and rich oxygen vacancies as well as abundant medium-strength CO2 adsorption sites. As a result, under the GHSV of 120000 mL/g·h and 150000 mL/g·h, Ni/SiO2@4ZrO2 displayed a considerable hydrogenation activity and significantly higher selectivity to CO, compared with the Ni/SiO2 catalyst as a reference. During stability tests, Ni/SiO2@4ZrO2 also showed a superior catalytic stability with a steady 100 % CO selectivity, carried out at 600 °C for 72 h. This work provided a novel strategy of designing a core-shell catalyst for CO2 RWGS reaction, and was expected to be put into use in other multiphase reaction process.

Advancements in green diesel production for energy sustainability: a comprehensive bibliometric analysis

Green diesel as a second-generation biofuel has received enormous attention owing to the huge demand for renewable fuel for addressing the net zero target in 2050. This study examines the development of green diesel research through a bibliometric analysis. The state-of-the-art green diesel research is studied based upon 1285 documents (1153 articles and 132 reviews) retrieved from the Scopus database related to the used keywords. The analysis focused on three categories: publication outcomes, most cited papers, and research area identification. The VOSviewer and RStudio (bibliometrix) were applied to analyse the data, rationalized within the framework of author, affiliation, country, citation analysis, cross-dimensional keyword analysis, research streams, and research gaps. The general result of the study highlighted a continuous incline in article numbers classified into three stages: initiation, exploration, and elevation. Those articles were mainly published in bioenergy-themed journals, including Fuel, Energy & Fuels, and Renewable and Sustainable Energy Reviews. Taufiq-Yap Yun Hin is the highest contributor with 41 articles, and Fuel published 110 articles. The rapid growth of green diesel was also inferred by the extensive spread of research maps worldwide. Amid those swift developments, the state of the art on green diesel through bibliometric analysis is not available to the best of our knowledge as far. Subsequently, this review aims to display the state of the art, research gap, and future forecast of green diesel research.

Porous Structure Fibers Based on Multi-Element Heterogeneous Components for Optimized Electromagnetic Wave Absorption and Self-Anticorrosion Performance

The excellent performance of electromagnetic wave absorbers primarily depends on the coordination among components and the rational design of the structure. In this study, a series of porous fibers with carbon nanotubes uniformly distributed in the shape of pine leaves are prepared through electrospinning technique, one-pot hydrothermal synthesis, and high-temperature catalysis method. The impedance matching of the nanofibers with a porous structure is optimized by incorporating melamine into the spinning solution, as it undergoes gas decomposition during high-temperature calcination. Moreover, the electronic structure can be modulated by controlling the NH4F content in the hydrothermal synthesis process. Ultimately, the Ni/Co/CrN/CNTs-CF specimen (P3C NiCrN12) exhibited superior performance, while achieving a minimum reflection loss (RLmin) of -56.18 dB at a thickness of 2.2 mm and a maximum absorption bandwidth (EABmax) of 5.76 GHz at a thickness of 2.1 mm. This study presents an innovative approach to fabricating lightweight, thin materials with exceptional absorption properties and wide bandwidth by optimizing the three key factors influencing electromagnetic wave absorption performance.

Biomass as an alternative feedstock to oleochemicals

The huge demands for petrochemicals have led to a rapid increase in the production of these fossil-based derivatives. Biomass represents a promising feedstock for addressing the challenges related to petrochemicals in terms of the necessity to apply renewable sources and the need to decrease carbon emissions. Among the natural biomass products, most studies have attempted to upgrade natural oils owing to their promising advantages of worldwide availability, low-cost processing, and built-in functionality. This paper discusses the upgradation of natural oils to the most beneficial oleochemicals, including fatty acids, fatty alcohols, and fatty acid methyl esters. This review also covers the utility, physico-chemical properties, and the production processes for such materials. The interconnected reaction routes to produce oleochemicals and the affecting parameters (catalyst design, temperature, and pressure) are also elucidated. Furthermore, this article discusses the future perspective of oleochemicals based on their development in recent years.

A Comparative Study of Hydrothermally Leached Al3TM and Al3TM-Rh (TM=Zr, V, Ce) Intermetallic Compounds for Catalytic Oxidation of Carbon Monoxide

Rise of the mute assassin "carbon monoxide (CO)" levels impact all aerobic life. The elevated rates of CO concentration endure climatic and geographical characteristics that exacerbate air pollution. Herein, a simple approach for hydrothermal leaching (HyTL) of Al3TM-Rh0.5 (Target material (TM)=Zr, V, Ce) and Al3TM (TM=Zr, V, Ce) intermetallic compounds produces leached products of ZrO2, VO2, and CeO2 with Rhodium (Rh) as an active component. The characterization result reveals the HyTL process and the presence of the active Rh element that elevated the performance of HyTL-Al3Zr-Rh0.5 towards CO conversion compared to other samples. Further, the cubic ZrO2 phase selectively forms after HyTL at 130 °C even though the formation of the cubic ZrO2 phase takes place at a high temperature. Moreover, the presence of Rh promotes higher catalytic activity in all the cases with low temperatures. The advancement in the present study towards the catalytic oxidation of CO over the hydrothermally leached ZrO2-Rh nanocatalyst guarantees the perspective of the aggregation-activation process.

Crystalline modulation of zirconia for efficient nitrate reduction to ammonia under ambient conditions

Zirconia as a polycrystalline catalyst can be effectively tuned by doping low-valence elements and meanwhile form abundant oxygen vacancies. Herein, the crystalline structures of zirconia are modulated by scandium doping and proposed as a robust catalyst for nitrate reduction to ammonia. The tetragonal zirconia achieves a maximum ammonia yield of 16.03 mg h-1 mgcat.-1, superior to the other crystal forms. DEMS tests unveil the reaction pathway and theoretical calculations reveal the low free energy of -0.22 eV for nitrate adsorption at the tetragonal zirconia.

Cobalt catalyzed ethane dehydrogenation to ethylene with CO2: Relationships between cobalt species and reaction pathways

TiO2, ZrO2 and a series of TiO2-ZrO2 (TxZ1, x means the atomic ratio of Ti/Zr = 10, 5, 1, 0.2 and 0.1) composite oxide supports were prepared through co-precipitation, and then 3 wt% Co was loaded through wetness impregnation methods. The obtained 3 wt% Co/TiO2 (3CT), 3 wt% Co/ZrO2 (3CZ) and 3 wt% Co/TxZ1 (3CTxZ1) catalysts were evaluated for the oxidative ethane dehydrogenation reaction with CO2 (CO2-ODHE) as a soft oxidant. 3CT1Z1 catalyst exhibits excellent catalytic properties, with C2H4 yield, C2H6 conversion and CO2 conversion about 24.5 %, 33.8 % and 18.0 % at 650 °C, respectively. X-Ray Diffraction (XRD), in-situ Raman, UV-vis diffuse reflectance spectra (UV-vis DRS), H2 temperature-programmed reduction (H2-TPR), Electron paramagnetic resonance (EPR) and quasi in-situ X-ray Photoelectron Spectroscopy (XPS) have been utilized to thoroughly characterize the investigated catalysts. The results revealed that 3CT1Z1 produced TiZrO4 solid solution with more metal defect sites and oxygen vacancies (Ov), promoting the formation of Co2+-TiZrO4 structure. Furthermore, the presence of Ov and Ti3+can facilitate the high dispersion and stabilization of Co2+, as well as suppressing the severe reduction of Co2+, leading to superior ethane oxidative dehydrogenation activity. Besides, less Co0 is beneficial to ODHE reaction, because of its promotion effects for reverse water gas shift reaction; however, more Co0 results in dry reforming reaction (DRE). This work will shed new lights for the design and preparation of highly efficient catalysts for ethylene production.

Efficient Solar-Driven CO2 Methanation and Hydrogen Storage Over Nickel Catalyst Derived from Metal-Organic Frameworks with Rich Oxygen Vacancies

Solar-driven photothermal conversion of carbon dioxide (CO2 ) to methane (CH4 ) is a promising approach to remedy energy shortage and climate changes, where highly efficient photothermal catalysts for CO2 methanation urgently need to be designed. Herein, nickel-based catalysts (Ni/ZrO2 ) derived from metal-organic frameworks (MOFs) are fabricated and studied for photothermal CO2 methanation. The optimized catalyst 50Ni/ZrO2 achieves a stable CH4 production rate of 583.3 mmol g-1  h-1 in a continuous stability test, which is almost tenfold higher than that of 50Ni/C-ZrO2 synthesized via commercial ZrO2 . Physicochemical properties indicate that 50Ni/ZrO2 generates more tetragonal ZrO2 and possesses more oxygen vacancies (OVs) as well as enhanced nickel-ZrO2 interaction. As a result, 50Ni/ZrO2 exhibits the strong abilities of light absorption and light-to-heat conversion, superior adsorption capacities of reactants (H2 , CO2 ), and an intermediate product (CO), which finally boosts CH4 formation. This work provides an efficient strategy to design a photothermocatalyst of CO2 methanation through utilizing MOFs-derived support.

Two-dimensional AlN/TMO van der Waals heterojunction as a promising photocatalyst for water splitting driven by visible light

In this study, the photocatalytic properties of AlN/TMO heterojunctions formed by coupling MoO2 and WO2 of transition metal oxides with AlN are studied in detail using first-principles calculations with the aim of finding efficient and low-cost photocatalysts for water splitting to produce hydrogen to reduce environmental pollution. The AIMD, phonon spectrum, and elastic constants demonstrated the thermodynamic, kinetic, and mechanical stabilities of the AlN/TMO heterojunction. The results showed that the AlN/MoO2 (1.55 eV) and AlN/WO2 (1.99 eV) heterojunctions have typical type-II energy band arrangements, which can effectively promote the separation of photogenerated electrons and hole pairs. Meanwhile, the AlN/MoO2 heterojunction showed excellent carrier mobilities (electron, 250.05 cm2 V-1 S-1 and hole, 45 467.07 cm2 V-1 S-1), which greatly exceeded those of each component. The AlN/WO2 heterojunction showed an excellent HER (-0.07 eV) performance, which was close to the expected value. For the AlN/WO2 heterojunction, a suitable band gap value, excellent HER, and other properties indicated that it has the potential to become a new candidate for photocatalytic water splitting. Our study enriches the theoretical research of transition metal oxide materials and wide-band gap materials by providing a reference direction for the design of reasonably high-quality photocatalysts.

Oxygen Vacancy-Induced Metal-Support Interactions in AuPd/ZrO2 Catalysts for Boosting 5-Hydroxymethylfurfural Oxidation

The construction of strong metal-support interactions in oxide-supported noble metal nanocatalysts has been considered an emerging and efficient way in improving catalytic performance in biomass-upgrading reactions. Herein, a citric acid (CA)-assisted synthesized ZrO2 layer with improved oxygen vacancy (Ov) concentrations on a natural clay mineral of halloysite nanotubes (HNTs) was designed. Moreover, AuxPdy/ZrO2@HNTs-zCA catalysts were prepared by loading AuPd bimetal and employed for aerobic oxidation of the lignocellulosic biomass-derived 5-hydroxymethylfurfural (HMF) platform to the bioplastic monomer 2,5-furandicarboxylic acid (FDCA) with water as the solvent. The results of catalytic experiments revealed that the Au3Pd1/ZrO2@HNTs-1.0CA catalyst exhibited excellent catalytic activity at 0.5 MPa O2, with a satisfactory FDCA yield of 99.5% and outstanding FDCA formation rate of 1057.9 mmol·g-1·h-1. The improved Ov concentration in the ZrO2 support enhanced the adsorption and activation ability of the catalyst for O2, and a higher Lewis acid concentration provided a stronger adsorption ability of the catalyst for reaction substrates. Besides, the synergistic effect of AuPd bimetallic nanoparticles steered the tandem oxidation of aldehyde and alcohol groups in HMF and accelerated the rate-determining step. More importantly, the relationship between the Ov concentration and catalytic performance also demonstrated that the enhanced catalytic activity for HMF oxidation was mainly attributed to the active interface of AuPd-ZrOx. This work offers fresh insights into rationally designing oxygen vacancy-driven strong interactions between the oxide support and noble nanoparticles for the catalytic upgrade of biomass platform chemicals.

Activating lattice oxygen of single-layer ZnO for the catalytic oxidation reaction

Tuning an oxide/metal interface is of critical importance for the performance enhancement of many heterogeneous catalytic reactions. However, catalytic oxidation occurring at the interface between non-reducible oxide and metal has been challenging, since non-reducible oxides hardly lose their lattice oxygen (O_L) or dissociate O₂ from the gas phase. In this work, a ZnO monolayer film on Au(111) is used as an inverse catalyst to investigate CO oxidation occurring at the ZnO/Au(111) interface via high pressure scanning tunneling microscopy. Surface science experiments indicate that oxygen intercalation under the ZnO monolayer film, termed ZnO/O/Au(111), can be achieved via a surface reaction with 1 × 10^-6 mbar O₃. Subsequent exposure of the formed ZnO/O/Au(111) surface to mbar CO at room temperature leads to the recovery of the pristine ZnO/Au(111) surface. Theoretical calculations reveal that O_L adjacent to intercalated oxygen (O_int) is activated due to the O_L-Zn-O_int bonding and surface corrugation, which can be directly involved in CO oxidation. Subsequently, O_int migrates to the formed oxygen vacancy from the subsurface resuming the pristine ZnO structure. These results thus reveal that oxygen intercalation underneath single-layer ZnO will strongly boost the oxidation reaction via activating adjacent lattice oxygen atoms.

Influence of Natural Mordenite Activation Mode on Its Efficiency as Support of Nickel Catalysts for Biodiesel Upgrading to Renewable Diesel

In the present work, natural mordenite originated from volcanic soils in Greek islands, activated using HCl solution and HCl solution followed by NaOH solution, was used as support for preparing two metallic nickel catalysts (30 wt.% Ni). The catalysts were thoroughly characterized (XRF, N₂ adsorption-desorption, SEM, XRD, TEM, H₂-TPR, NH₃-TPD) and evaluated for biodiesel upgrading to green (renewable) diesel. Double activation of natural mordenite optimized its supporting characteristics, finally resulting in a supported nickel catalyst with (i) enhanced specific surface area (124 m² g^-1) and enhanced mean pore diameter (14 nm) facilitating mass transfer; (ii) easier nickel phase reduction; (iii) enhanced Ni⁰ dispersion and thus high active surface; (iv) balanced population of moderate and strong acid sites; (v) resistance to sintering; and (vi) low coke formation. Over the corresponding catalyst, the production of a liquid consisting of 94 wt.% renewable diesel was achieved, after 9 h of reaction at 350 °C and 40 bar H₂ pressure, in a semi-batch reactor under solvent-free conditions.

Selectivity of reaction pathways for green diesel production towards biojet fuel applications

Green diesel is the second generation biofuel with the same structure as fossil fuels (alkanes), allowing this biofuel to provide excellent fuel properties over biodiesel such as higher energy content and lower hazardous gas emission. Generally, green diesel can be produced through the deoxygenation/hydrogenation of natural oil and/or its derivatives at 200-400 °C and 1-10 MPa over supported metal catalysts. This process comprises of three reaction pathways: hydrodeoxygenation, decarboxylation, and decarbonylation. The extent to which these three different pathways are involved is strongly influenced by the catalyst, pressure, and temperature. Subsequently, the determination of catalyst and reaction condition plays a significant role owing to the feasibility of the process and the economic point of view. This article emphasizes the reaction pathway of green diesel production as well as the parameters influencing the predominant reaction route.

Chromium oxide modified mesoporous zirconium dioxide: Efficient heterogeneous catalysts for the synthesis of 5-hydroxymethylfurfural

Achieving the highly efficient carbohydrates conversion to 5-hydroxymethylfurfural (5-HMF) is a promising method to achieve green and sustainable development. However, most currently reported strategies are energy consuming and the 5-HMF yield is relatively lower in the aqueous phase. Herein, a facile method was reported to obtain the effective Cr/ZrO2 catalysts with high acidity and their catalytic performances were investigated for catalyzing fructose to 5-HMF at different temperatures and times. With the catalysis of 15% Cr/ZrO2 catalyst, the highest fructose conversion of 98%, 5-HMF yield of 48.8%, and 5-HMF selectivity of 49.8% are achieved in green solvent with good recyclability. The possible reaction process of the improved catalysis performance is attributed to the highly crystalline and strong acidity of the Cr/ZrO2 catalyst. The Lewis acid sites could increase the overall rate of fructose conversion by promoting side reactions and might suppressing fructose to glucose isomerization. In addition, Cr leakage during the reaction might act as the Bronsted acids to catalyze the fructose dehydration to 5-HMF. The reported method of introducing chromium oxides into ZrO2 catalyst will open a new avenue to promote the practical application of biomass and sustainable development in the future.

Algal biomass valorisation to high-value chemicals and bioproducts: Recent advances, opportunities and challenges

Algae are considered promising biomass resources for biofuel production. However, some arguments doubt the economical and energetical feasibility of algal cultivation, harvesting, and conversion processes. Beyond biofuel, value-added bioproducts can be generated via algae conversion, which would enhance the economic feasibility of algal biorefineries. This review primarily focuses on valuable chemical and bioproduct production from algae. The methods for effective recovery of valuable algae components, and their applications are summarized. The potential routes for the conversion of lipids, carbohydrates, and proteins to valuable chemicals and bioproducts are assessed from recent studies. In addition, this review proposes the following challenges for future algal biorefineries: (1) utilization of naturally grown algae instead of cultivated algae; (2) fractionation of algae to individual components towards high-selectivity products; (3) avoidance of humin formation from algal carbohydrate conversion; (4) development of strategies for algal protein utilisation; and (5) development of efficient processes for commercialization and industrialization.

Effect of calcination temperature on the Cu–ZrO2 interfacial structure and its catalytic behavior in the hydrogenation of dimethyl oxalate

The 5 wt% Cu/ZrO2 catalysts showed satisfying performance in DMO hydrogenation to EG via simply tuning the calcination temperature. The synergistic effect of the Cu0–Cu+–ZrO2 interface in activating H2 molecules and carbonyl bonds was elucidated.