Plasma-Assisted Surface Interactions of Pt/CeO2 Catalyst for Enhanced Toluene Catalytic Oxidation

A comprehensive review of oxygen vacancy modified photocatalysts: synthesis, characterization, and applications

Photocatalytic technology is a novel approach that harnesses solar energy for efficient energy conversion and effective pollution abatement, representing a rapidly advancing field in recent years. The development and synthesis of high-performance semiconductor photocatalysts constitute the pivotal focal point. Oxygen vacancies, being intrinsic defects commonly found in metal oxides, are extensively present within the lattice of semiconductor photocatalytic materials exhibiting non-stoichiometric ratios. Consequently, they have garnered significant attention in the field of photocatalysis as an exceptionally effective means for modulating the performance of photocatalysts. This paper provides a comprehensive review on the concept, preparation, and characterization methods of oxygen vacancies, along with their diverse applications in nitrogen fixation, solar water splitting, CO2 photoreduction, pollutant degradation, and biomedicine. Currently, remarkable progress has been made in the synthesis of high-performance oxygen vacancy photocatalysts and the regulation of their catalytic performance. In the future, it will be imperative to develop more advanced in situ characterization techniques, conduct further investigations into the regulation and stabilization of oxygen vacancies in photocatalysts, and comprehensively comprehend the mechanism underlying the influence of oxygen vacancies on photocatalysis. The engineering of oxygen vacancies will assume a pivotal role in the realm of semiconductor photocatalysis.

Regulating Pt-based noble metal catalysts for the catalytic oxidation of volatile organic compounds: a mini review

Volatile organic compounds (VOCs) are an important class of environmental pollutants, and there is much interest in China to eliminate such pollutants. Noble metal catalysts have long been a family of catalysts with high efficiency and good low-temperature catalytic activity. As a representative of the noble metals, Pt has been widely used. This paper reviews the research trend of Pt-based catalysts for the catalytic oxidation of VOCs, and it compares several important components of Pt-based catalysts. The size of Pt particles, supported carriers, and reaction mechanism are reviewed. Toluene in VOCs is the main research subject. The activity, stability, water resistance, and selectivity of a series of Pt-based catalysts are summarized.

Unravelling the correlation of dielectric barrier discharge power and performance of Pt/CeO2 catalysts for toluene oxidation

Two “volcano” peaks in the relevant activity curve showcased that plasma discharge power had a significant impact on the activity of Pt/CeO2-Px catalysts and modulating discharge power could be regarded as an efficient method to optimize catalyst performance.

Recent advances in the abatement of volatile organic compounds (VOCs) and chlorinated-VOCs by non-thermal plasma technology: A review

Most of the volatile organic compounds (VOCs) and especially the chlorinated volatile organic compounds (Cl-VOCs), are regarded as major pollutants due to their properties of volatility, diffusivity and toxicity which pose a significant threat to human health and the eco-environment. Catalytic degradation of VOCs and Cl-VOCs to harmless products is a promising approach to mitigate the issues caused by VOCs and Cl-VOCs. Non-thermal plasma (NTP) assisted catalysis is a promising technology for the efficient degradation of VOCs and Cl-VOCs with higher selectivity under relatively mild conditions compared with conventional thermal catalysis. This review summarises state-of-the-art research of the in plasma catalysis (IPC) of VOCs degradation from three major aspects including: (i) the design of catalysts, (ii) the strategies of deep catalytic degradation and by-products inhibition, and (iii) the fundamental research into mechanisms of NTP activated catalytic VOCs degradation. Particular attention is also given to Cl-VOCs due to their characteristic properties of higher stability and toxicity. The catalysts used for the degradation Cl-VOCs, chlorinated by-products formation and the degradation mechanism of Cl-VOCs are systematically reviewed in each chapter. Finally, a perspective on future challenges and opportunities in the development of NTP assisted VOCs catalytic degradation were discussed.

Surface Modification by Amino Group Inducing for Highly Efficient Catalytic Oxidation of Toluene over a Pd/KIT-6 Catalyst

Toluene is one of the typical volatile organic compounds in industry, particularly in energy and fuels production processes, which is required to be eliminated effectively to protect the environment. Catalytic oxidation of toluene is widely studied for its high efficiency, and rational design and synthesis of metal catalysts are keys for toluene oxidation. In this study, an efficient catalyst was designed and synthesized by introducing -NH₂ groups on the ordered mesoporous silica (KIT-6) surface to anchor and disperse Pd species, leading to Pd nanoparticles being highly dispersed with uniform particle size distribution. Meanwhile, it was found that the introduction of -NH₂ made Pd centers present an electron-rich state, and the active Pd centers could activate O₂ molecules to generate more reactive oxygen species and promote the conversion of toluene, which was verified by in situ XPS and O₂-TPD characterization. Compared with the catalysts prepared by an impregnation method, the catalytic performance of the Pd/NH₂-KIT-6 (0.5 wt %) catalyst was significantly improved. A conversion of 90% for toluene (2400 ppm, 24,000 mL·g^-1·h^-1) was achieved at 171 °C, and the toluene conversion was maintained above 90% for 900 min, displaying the excellent activity and stability of the Pd/NH₂-KIT-6 catalyst.

A review of the advances in catalyst modification using nonthermal plasma: Process, Mechanism and Applications

With the continuous development of catalytic processes in chemistry, biology, organic synthesis, energy generation and many other fields, the design of catalysts with novel properties has become a new paradigm in both science and industry. Nonthermal plasma has aroused extensive interest in the synthesis and modification of catalysts. An increasing number of researchers are using plasma for the modification of target catalysts, such as modifying the dispersion of active sites, regulating electronic properties, enhancing metal-support interactions, and changing the morphology. Plasma provides an alternative choice for catalysts in the modification process of oxidation, reduction, etching, coating, and doping and is especially helpful for unfavourable thermodynamic processes or heat-sensitive reactions. This review focuses on the following points: (i) the fundamentals behind the nonthermal plasma modification of catalysts; (ii) the latest research progress on the application of plasma modified catalysts; and (iii) main challenges in the field and a vision for future development.

Synergistic degradation of fluorene in soil by dielectric barrier discharge plasma combined with P25/NH2-MIL-125(Ti)

Plasma techniques to degrade pollutants are generally more efficient than conventional methods, but exist some problems such as high energy consumption, incomplete degradation of pollutants, and secondary pollution caused by highly toxic intermediates. In this study, the dielectric barrier discharge plasma (DBDP) combined with the Ti-based metal organic frameworks (MOFs) catalysts (P25/NH₂-MIL-125(Ti)) was used to degrade fluorene in the soil. The synergistic treatment technique used in soil remediation can realize a green and promising treatment efficiency with relatively low energy consumption. Compared with DBDP system alone, the synergetic treatment system of DBDP and P25/NH₂-MIL-125(Ti) considerably increased the degradation efficiency of fluorene in the soil to above 90% at 10 min, even with a relatively low discharge voltage (5 kV). The synergistic treatment system achieved 88.8% of fluorene mineralization at 60 min. Optical emission spectroscopy and electron paramagnetic resonance spectroscopy both showed that •OH and •O₂^- played an important role in the synergetic treatment system. Nine main intermediates were identified using gas chromatography-mass spectrometry and Fourier transform infrared analysis. The main degradation of fluorine in soil was caused by the electronic transition of the catalytic material excited by DBDP, and finally mineralized into CO₂ and H₂O. The fluorene and its toxic intermediates were effectively removed. This study provides an insight for achieving high efficiency and environmentally friendly application perspective in soil remediation.

Construction of nanorod structure confined Pt@CeO2 catalyst by in-situ encapsulation strategy for low temperature catalytic oxidation of toluene

In this work, the Pt@CeO2 catalyst with the nanorod structure (Pt@CeO2-R) and the bunch structure (Pt@CeO2-B) were synthesized through in situ encapsulation strategy of Pt species in Ce-MOFs, respectively. It is discovered that the Pt@CeO2-R catalyst owned the best catalytic performance for toluene catalytic combustion, and this situation was mainly caused by the confinement of Pt nanoparticles in Ce-MOFs, which was related to the chemical state of Pt species, redox ability, and the amount of active oxygen species. Among them, the Pt@CeO2-R catalyst owns more Ce3+ species, rich Pt4+ species, and abundant active oxygen species due to the existence of confined structure, which were conducive to promote catalytic oxidation of toluene. In addition, the Pt@CeO2-R catalyst also exhibited more redox ability, which may speed up the catalytic reaction rates. On the contrary, the Pt/CeO2-R catalyst was synthesized through a simple impregnation method, and exhibited the poor activity for toluene catalytic combustion due to poor Pt4+ species and active oxygen species. Therefore, this work provides a feasible experimental basis for the study of different morphologies and encapsulated metal particles.

Current progress on catalytic oxidation of toluene: a review

Toluene is one of the pollutants that are dangerous to the environment and human health and has been sorted into priority pollutants; hence, the control of its emission is necessary. Due to severe problems caused by toluene, different techniques for the abatement of toluene have been developed. Catalytic oxidation is one of the promising methods and effective technologies for toluene degradation as it oxidizes it to CO₂ and does not deliver other pollutants to the environment. This paper highlights the recent progressive advancement of the catalysts for toluene oxidation. Five categories of catalysts, including noble metal catalysts, transition metal catalysts, perovskite catalysts, metal-organic frameworks (MOFs)-based catalysts, and spinel catalysts reported in the past half a decade (2015-2020), are reviewed. Various factors that influence their catalytic activities, such as morphology and structure, preparation methods, specific surface area, relative humidity, and coke formation, are discussed. Furthermore, the reaction mechanisms and kinetics for catalytic oxidation of toluene are also discussed.

Plasma-Induced Catalyst Support Defects for the Photothermal Methanation of Carbon Dioxide

The presence of defects in a catalyst support is known to benefit catalytic activity. In this work, a He-plasma treatment-based strategy for introducing and stabilising defects on a Ni/TiO₂ catalyst for photothermal CO₂ hydrogenation was established. The impact of pretreatment step sequence—which comprised He-plasma treatment and reduction/passivation—on defect generation and stabilisation within the support was evaluated. Characterisation of the Ni/TiO₂ catalysts indicated that defects created in the TiO₂ support during the initial plasma treatment stage were then stabilised by the reduction/passivation process, (P-R)Ni/TiO₂. Conversely, performing reduction/passivation first, (R-P)Ni/TiO₂, invoked a resistance to subsequent defect formation upon plasma treatment and consequently, poorer photothermal catalytic activity. The plasma treatment altered the metal-support interaction and ease of catalyst reduction. Under photothermal conditions, (P-R)Ni/TiO₂ reached the highest methane production in 75 min, while (R-P)Ni/TiO₂ required 165 min. Decoupling the impacts of light and heat indicated thermal dominance of the reaction with CO₂ conversion observed from 200 °C onwards. Methane was the primary product with carbon monoxide detected at 350 °C (~2%) and 400 °C (~5%). Overall, the findings demonstrate the importance of pretreatment step sequence when utilising plasma treatment to generate active defect sites in a catalyst support.

Non-Thermal Plasma-Modified Ru-Sn-Ti Catalyst for Chlorinated Volatile Organic Compound Degradation

Chlorinated volatile organic compounds (CVOCs) are vital environmental concerns due to their low biodegradability and long-term persistence. Catalytic combustion technology is one of the more commonly used technologies for the treatment of CVOCs. Catalysts with high low-temperature activity, superior selectivity of non-toxic products, and resistance to chlorine poisoning are desirable. Here we adopted a plasma treatment method to synthesize a tin-doped titania loaded with ruthenium dioxide (RuO2) catalyst, possessing enhanced activity (T90%, the temperature at which 90% of dichloromethane (DCM) is decomposed, is 262 °C) compared to the catalyst prepared by the conventional calcination method. As revealed by transmission electron microscopy, X-ray diffraction, N2 adsorption, X-ray photoelectron spectroscopy, and hydrogen temperature-programmed reduction, the high surface area of the tin-doped titania catalyst and the enhanced dispersion and surface oxidation of RuO2 induced by plasma treatment were found to be the main factors determining excellent catalytic activities.

Platinum-Decorated Ceria Enhances CO2 Electroreduction in Solid Oxide Electrolysis Cells

CO₂ electroreduction by solid oxide electrolysis cells (SOECs) can not only attenuate the greenhouse effect, but also convert surplus electrical energy into chemical energy. The adsorption and activation of CO₂ on the cathode play an important role in the SOEC performance. La_0.6 Sr_0.4 Co_0.2 Fe_0.8 O_3-δ -Ce_0.8 Sm_0.2 O_2-δ (LSCF-SDC; SDC=samarium-doped ceria) is a promising SOEC cathode. However, its electrocatalytic activity still needs to be improved. In this study, Pt/SDC interfaces are constructed by decorating Pt nanoparticles onto the SDC surface. Electrochemical measurements indicate that the polarization resistance of the SOEC is decreased from 0.308 to 0.120 Ω cm² , and the current density is improved from 0.913 to 1.420 A cm^-2 at 1.6 V and 800 °C. Physicochemical characterizations suggest that construction of the Pt/SDC interfaces increases the oxygen vacancy concentration on the cathode and boosts CO₂ adsorption and dissociation, which leads to enhanced CO₂ electroreduction performance in SOECs.

Unveiling the Electronic Interaction in ZnO/PtO/Pt Nanoarrays for Catalytic Detection of Triethylamine with Ultrahigh Sensitivity

The detection of harmful volatile organic compounds is of great significance to environmental quality and human health. However, it still remains a challenge to achieve high detection sensitivity at a relatively low temperature. Herein, an ultrasensitive catalytic sensor for the detection of triethylamine (TEA) based on ZnO/PtO/Pt nanoarray thin films was realized. Sensor measurements reveal that the PtO/Pt sensitizer dramatically reduces the working temperature from 195 °C of a pristine ZnO sensor to 125 °C of ZnO/PtO/Pt sensors. The ZnO/PtO/Pt sensors exhibit an extremely high response of 3513 to 50 ppm TEA, which is three orders of magnitude higher than that of pristine ZnO. Meanwhile, an ultralow limit of detection of 8.3 ppb is achieved. The outstanding performances are superior to those in most previous reports on TEA detection. Mechanistic investigations reveal that the outstanding performances are ascribed to the strong electronic interaction between PtO and ZnO and the catalytic spillover effect of Pt.

Trimesoyl Chloride-Melamine Copolymer-TiO2 Nanocomposites as High-Performance Visible-Light Photocatalysts for Volatile Organic Compound Degradation

Benzene is a typical volatile organic compound (VOC) and is found widely in industrial waste gases. In this study, trimesoyl chloride-melamine copolymer (TMP)-TiO2 nanocomposites with excellent photocatalytic efficiency in visible-light degradation of gas-phase benzene were synthesized via an in situ hydrothermal synthesis. The optimal conditions for TMP-TiO2 nanocomposite synthesis were determined by orthogonal experiments. The structural, physiochemical, and optoelectronic properties of the samples were studied by various analytical techniques. Ultraviolet-visible diffuse reflectance spectroscopy and surface photovoltage spectra showed that the positions of the light-absorbance edges of the TMP-TiO2 nanocomposites were sharply red-shifted to the visible region relative to those of unmodified TiO2. The most efficient TMP-TiO2 nanocomposite was used for photocatalytic oxidative degradation of gas-phase benzene (initial concentration 230 mg m−3) under visible-light irradiation (380–800 nm); the degradation rate was 100% within 180 min. Under the same reaction conditions, the degradation rates of unmodified TiO2 (hydrothermally synthesized TiO2) and commercial material Degussa P25 were 19% and 23.6%, respectively. This is because the Ti–O–N and Ti–O–C bonds in TMP-modified TiO2 reduce the band gap of TMP-TiO2. The amide bonds in the TMP decrease the TiO2 nanoparticle size and thus increased the specific surface area. The conjugated structures in the TMP provide abundant active sites for trapping photogenerated electrons and promote the separation and transfer of photogenerated electrons and holes.