Revealing the correlation between adsorption energy and activation energy to predict the catalytic activity of metal oxides for HMX using DFT

Traditional selection of combustion catalysis is time-consuming and labor-intensive.Theoretical calculation is expected to resolve this problem.The adsorption energy of HMX and O atoms on 13 metal oxides was calculated using DMol3,since HMX and O are key substances in decomposition process.And the relationship between the adsorption energy of HMX,O on metal oxides(TiO_(2),Al_(2)O_(3),PbO,CuO,Fe_(2)O_(3),Co_(3)O_(4),Bi_(2)O_(3),NiO)and experimental T30 values(time required for the decomposition depth of HMX to reach 30%)was depicted as volcano plot.Thus,the T30 values of other metal oxides was predicted based on their adsorption energy on volcano plot and validated by previous experimental data.Further,the adsorption energy of HMX on ZrO_(2)and MnO_(2)was predicted based on the linear relationship between surface energy and adsorption energy,and T30 values were estimated based on volcano plot.The apparent activation energy data of HMX/MgO,HMX/SnO_(2),HMX/ZrO_(2),and HMX/MnO_(2)obtained from DSC experiments are basically consistent with our predicted T30 values,indicating that it is feasible to predict the catalytic activity based on the adsorption calculation,and it is expected that these simple structural properties can predict adsorption energy to reduce the large quantities of computation and experiment cost.

Recent progress on transition metal oxides and carbon-supported transition metal oxides as catalysts for thermal decomposition of ammonium perchlorate

As a main oxidizer in solid composite propellants,ammonium perchlorate(AP)plays an important role because its thermal decomposition behavior has a direct influence on the characteristic of solid composite propellants.To improve the performance of solid composite propellant,it is necessary to take measures to modify the thermal decomposition behavior of AP.In recent years,transition metal oxides and carbon-supported transition metal oxides have drawn considerable attention due to their extraordinary catalytic activity.In this review,we highlight strategies to enhance the thermal decomposition of AP by tuning morphology,varying the types of metal ion,and coupling with carbon analogue.The enhanced catalytic performance can be ascribed to synergistic effect,increased surface area,more exposed active sites,and accelerated electron transportation and so on.The mechanism of AP decomposition mixed with catalyst has also been briefly summarized.Finally,a conclusive outlook and possible research directions are suggested to address challenges such as lacking practical application in actual formulation of solid composite propellant and batch manufacturing.

Co-Ce-Ni Ternary Metal Oxide Modified N-activated Carbon:The Superior Low Temperature NH3-SCR Performance

Introducing reduced metal and nitrogen species is a powerful strategy to improve the reactivity of carbon-based materials for selective catalytic reduction of NO_(x) with NH_(3).To further improve the NH_(3)-SCR performance of non-pitch coal activated coke(NPAC),a series of metal oxides(e.g.,Co,Ce,and Ni)were loaded on nitrogen modified NPAC.The outstanding performance of NPAC-N-CoCeNi as well as the superior SO_(2)-and H_(2)O-tolerate performance are attributed to the extra electrons caused by the modification of N species,and these extra electrons are more conducive to the electron transfer.More importantly,the interaction of the major active component Co^(3+)and the promoter catalysts CeO_(2),NiOx,or CoNiO_(2) can also increase the charge transfer and produce more oxygen vacancy and unsaturated chemical bonds,leading to improving the redox performance of NPAC-N-CoCeNi.In addition,the NH3-SCR reaction is promoted after the metal oxides co-doping mainly via the Mars-van-Krevelen mechanism.

Activated Carbons Containing Dispersed Metal Oxide Particles for Removal of Methyl Mercaptan in Air

Activated carbons containing dispersed metal oxide particles were prepared by carbonization of phenol resin containing metal compounds followed by steam activation. Acetylacetonates of Fe, Mn and V, and Cu nitrate were used as the sources of metals. The removal of a small amount of methyl mercaptan (CH3SH) in air with these activated carbons was tested in a flow system. Compared with activated carbons without metal oxides, the carbons exhibited high activity for the removal of CH3SH in air. In particular, activated carbon obtained from Novolac containing 5 wt% Cu showed excellent behavior over a long time.

Characterization of Metal Oxide-modified Walnut-shell Activated Carbon and Its Application for Phosphine Adsorption: Equilibrium, Regeneration, and Mechanism Studies

We prepared a kind of metal oxide-modified walnut-shell activated carbon(MWAC) by KOH chemical activation method and used for PH_3 adsorption removal. Meanwhile, the PH_3 adsorption equilibrium was investigated experimentally and fitted by the Toth equation, and the isosteric heat of PH_3 adsorption was calculated by the Clausius-Clapeyron Equation. The exhausted MWAC was regenerated by water washing and air drying. Moreover, the properties of five different samples were characterized by N_2 adsorption isotherm, SEM/EDS, XPS, and FTIR. The results showed that the maximum PH_3 equilibrium adsorption capacity was 595.56 mg/g. The MWAC had an energetically heterogeneous surface due to values of isosteric heat of adsorption ranging from 43 to 90 kJ/mol. The regeneration method provided an effective way for both adsorption species recycling and exhausted carbon regeneration. The high removal efficiency and big equilibrium adsorption capacity for PH_3 adsorption on the MWAC were related to its large surface area and high oxidation activity in PH_3 adsorption-oxidation to H_3 PO_4 and P_2 O_5. Furthermore, a possible PH_3 adsorption mechanism was proposed.

Catalysis of Active Carbon Supporting Transition Metal Oxides for Pyrotechnical Reagent with Potassium Perchlorate

In order to improve the pyrotechnical reagent with potassium perchlorate,composite catalyst of active carbon supporting transition metal oxides （TMO）,Fe2O3 and CuO,were prepared and added into pyrotechnical reagent with potassium perchlorate.Accelerating rate calorimeter （ARC） was used to study the catalysis of pyrotechnical reagent which is consisted of potassium perchlorate and composite catalyst.Composite catalyst of both Fe2O3 and CuO supported by active carbon can catalyze pyrotechnical reagent with potassium perchlorate.Furthermore,it can lower the apparent activation energy and accelerate the reaction with a smaller quantity than that with Fe2O3 and CuO.The maximal reaction rate of pyrotechnical reagent with potassium perchlorate mixed with Fe2O3/active carbon and CuO/active carbon is 8.31 min-1 and 9.13 min-1,which is 1.74 times and 1.91 times of pyrotechnical reagent mixed with no catalyst;time to maximal rate was 18.99 min and 1.96 min respectively,which is lower than pyrotechnical reagent mixed with no catalyst by 86.46% and 98.67% ;the apparent activation energy is 368.10 kJ·mol-1 and 325.29 kJ·mol-1,which is lower than pyrotechnical reagent mixed with no catalyst by 31.89% and 39.81% respectively.

Electron Donating Property and Catalytic Activity ofPerovskite-type Mixed Oxides (ABO_3) Consisting of Rare Earth and 3d Transition Metals

The catalytic activity of Perovskite-type mixed oxides (LaCoO3, PrCoO3 and SmCoO3) for the reduction of cyclohexanone to cyclohexanol with 2-propanol (Meerwein-PonndorfVerley reduction) has been studied. The data have been correlated with the surface electron donor properties of these mixed oxides

The catalytic activity of transition metal oxide nanoparticles on thermal decomposition of ammonium perchlorate

The catalytic proficiency of three MONs for AP thermal decomposition was studied in this work.A chemical co-precipitation method was used for synthesis of MONs(CuZnO,CoZnO,and NiZnO)and their characterization carried out by utilizing XRD,FTIR,and SEM.The TGA/DSC technique was employed for the investigation of the catalytic proficiency of MONs on the AP.The DSC data were used for measuring activation energy of catalyzed AP by using Ozawa,Kissinger,and Starink method.The MONs were much sensitive for AP decomposition,and the performance of AP decomposition was further improved.Among all the MONs,the CuZnO exhibits higher catalytic action than others and decomposition temperature of AP is descending around 117℃ by CuZnO.The reduction in the activation energy was noticed after the incorporation of MONs in AP.

Influence of alkali metal doping on surface properties and catalytic activity/selectivity of CaO catalysts in oxidative coupling of methane

Surface properties （viz. surface area, basicity/base strength distribution, and crystal phases） of alkali metal doped CaO （alkali metal/Ca= 0.1 and 0.4） catalysts and their catalytic activity/selectivity in oxidative coupling of methane （OCM） to higher hydrocarbons at different reaction conditions （viz. temperature, 700 and 750 ℃; CH4/O2 ratio, 4.0 and 8.0 and space velocity, 5140-20550 cm^3 ·g^-1·h^-1） have been investigated. The influence of catalyst calcination temperature on the activity/selectivity has also been investigated. The surface properties （viz. surface area, basicity/base strength distribution） and catalytic activity/selectivity of the alkali metal doped CaO catalysts are strongly influenced by the alkali metal promoter and its concentration in the alkali metal doped CaO catalysts. An addition of alkali metal promoter to CaO results in a large decrease in the surface area but a large increase in the surface basicity （strong basic sites） and the C2＋ selectivity and yield of the catalysts in the OCM process. The activity and selectivity are strongly influenced by the catalyst calcination temperature. No direct relationship between surface basicity and catalytic activity/selectivity has been observed. Among the alkali metal doped CaO catalysts, Na-CaO （Na/Ca = 0.1, before calcination） catalyst （calcined at 750 ℃）, showed best performance （C2＋ selectivity of 68.8% with 24.7% methane conversion）, whereas the poorest performance was shown by the Rb-CaO catalyst in the OCM process.

Catalytic hydrolysis of carbonyl sulfide over modified coal-based activated carbons by loading metal

A novel type of metal oxide/activated carbon catalyst was prepared by sol-gel method for the hydrolysis of carbonyl sulfide （COS）. The influences of the calcination temperature, additive content （2.5%-10.0% Fe2O3, mass fraction） and the basic density of the activation process were thoroughly investigated. The surface of catalysts was characterized by Boehm titration. The products were characterized by scanning electron microscopy （SEM）, X-ray diffractometry （XRD） and X-ray photoelectron spectroscopy （XPS）. The results show that catalysts with 2.5%-5.0% Fe2O3 after calcining at 500 ℃ have superior activity. The conversion rate of COS increases with increasing the relative density of basic capacity loaded onto activated carbon（AC）, and the activity follows the order： KOH〉Na2CO3 〉NaHCO3. Boehm titration data clearly show that the total acidity increases （from 0.06 to 0.48 mmol/g） and the basic groups decrease （from 0.78 to 0.56 mmol/g） after COS hydrolysis and H2S adsorption. The XPS results show that the product of HzS may be absorbed by the interaction with metal compounds and 02 to form sulfate （171.28 eV） and element sulfur （164.44 eV）, which lead to catalysts poisoning.

Density Functional Theory Studies on the Mechanism of Activation Formic Acid Catalyzed by Transition Metal Oxide MoO

This paper systematically studies the reaction mechanisms of formic acid catalyzed by transition metal oxide MoO. Three different reaction pathways of Routes I, Ⅱ and Ⅲ were found through studying the reaction mechanism of transition metal oxide MoO catalyzing the formic acid. The transition metal oxide MoO interacts with the C=O double bond to form chiral chain compounds（Routes I and Ⅱ） and metallic compound MoOH2（Route Ⅲ）. In this paper, we have studied the mechanisms of two addition reaction pathways and hydrogen abstraction reaction pathway. Routes I and Ⅱ are both addition reactions, and their products are two different chiral compounds MoO3CH2, which are enantiomeric to each other. In Route Ⅲ, metal compounds MoOH2 and CO2 are obtained from the hydrogen abstraction reaction. Among them, the hydrogen abstraction reaction occurring in Route Ⅲ is more likely to occur than the others. By comparing the results of previous studies on the reaction of MxOy-＋ ROH（M= Mo,W; R = Me, Et）, we found that the hydrogen abstraction mechanism is completely different from the mechanism of oxygen-containing organic compound catalyzed by MxOy.

Activation of Transition Metal(Fe,Co and Ni)-Oxide Nanoclusters by Nitrogen Defects in Carbon Nanotube for Selective CO_(2) Reduction Reaction

The electrochemical carbon dioxide reduction reaction(CO_(2)RR),which can produce value-added chemical feedstocks,is a proton-coupled-electron process with sluggish kinetics.Thus,highly efficient,cheap catalysts are urgently required.Transition metal oxides such as CoO_(x),FeO_(x),and NiO_(x)are low-cost,low toxicity,and abundant materials for a wide range of electrochemical reactions,but are almost inert for CO_(2)RR.Here,we report for the first time that nitrogen doped carbon nanotubes(N-CNT)have a surprising activation effect on the activity and selectivity of transition metal-oxide(MO_(x)where M=Fe,Ni,and Co)nanoclusters for CO_(2)RR.MO_(x)supported on N-CNT,MO_(x)/N-CNT,achieves a CO yield of 2.6–2.8 mmol cm−2 min−1 at an overpotential of−0.55 V,which is two orders of magnitude higher than MO_(x)supported on acid treated CNTs(MO_(x)/O-CNT)and four times higher than pristine N-CNT.The faraday efficiency for electrochemical CO_(2)-to-CO conversion is as high as 90.3%at overpotential of 0.44 V.Both in-situ XAS measurements and DFT calculations disclose that MO_(x)nanoclusters can be hydrated in CO_(2)saturated KHCO_(3),and the N defects of N-CNT effectively stabilize these metal hydroxyl species under carbon dioxide reduction reaction conditions,which can split the water molecules and provide local protons to inhibit the poisoning of active sites under carbon dioxide reduction reaction conditions.

Preparation of metal oxide doped ACNFs and their adsorption performance for low concentration SO_2

Metal oxide （TiO2 or Co304） doped activated carbon nanofibers （ACNFs） were prepared by electrospinning. These nanofibers were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and Brunner- Emmett-Teller method （BET）. The results show that the average diameters of ACNFs were within the range of 200-500 nm, and the lengths were several tens of micrometers. The specific surface areas were 1146.7 m2/g for TiO2-doped ACNFs and 1238.5 m2/g for Co304-doped ACNFs, respectively. The electrospun nanofibers were used for adsorption of low concentration sulfur dioxide （SO2）. The results showed that the adsorption rates of these ACNFs increased with an increase in SO2concentration. When the SO2 concentration was 1.0 μg/mL, the adsorption rates of TiO2-doped ACNFs and Co3Oa-doped ACNFs were 66.2% and 67.1%, respectively. The adsorption rate also increased as the adsorption time increased. When the adsorption time was 40 min, the adsorption rates were 67.6% and 69.0% for TiO2-doped ACNFs and Co304-doped ACNFs, respectively. The adsorption rate decreased as the adsorption temperature increased below 60℃, while it increased as the adsorption temperature increased to more than 60℃.

A palladium single-atom catalyst toward efficient activation of molecular oxygen for cinnamyl alcohol oxidation

Selective aerobic oxidation of alcohols under mild conditions is of great importance yet challenging,with the activation of molecular oxygen(O2)as a crucial capability of the catalysts.Herein,we demonstrate that an Al2O3-supported Pd single-atom catalyst leads to higher activity and selectivity compared to Pd nanoparticles for the oxidation of cinnamyl alcohol.The Al2O3 support used in this study is rich in coordinately unsaturated Al3+sites,which are apt for binding to Pd atoms through oxygen bridges and present a distinct metal-support interaction(MSI).The suitable MSI then leads to a unique electronic characteristic of the Pd single atoms,which can be confirmed via X-ray photoelectron spectroscopy,normalized X-ray absorption near-edge structure,and diffuse reflectance Fourier transform infrared spectroscopy.Moreover,this unique electronic state is proposed to be responsible for its high catalytic activity.With the help of in-situ UV-vis spectra and electron spin resonance spectra,a specific alcohol oxidation route with O2 activation mechanism is then identified.Active oxygen species behaving chemically like singlet-O2 are generated from the interaction of O2 with Pd1/Al2O3,and then oxidize the partially dehydrogenated intermediates produced by the adsorbed allylic alcohols and Pd atoms to the desired alkenyl aldehyde.This work provides a promising path for the design and development of high-activity catalysts for aerobic oxidation reactions.

Visible-Light-Active Noble-Metal Photocatalysts for Water Disinfection: A Review

The sanitary and environmental challenges posed by an ever growing economically and geographically diverse human population include the need for sustainable, inexpensive, scalable, and decentralized water treatment technologies that can supplement or replace conventional treatment methods. These challenges can be met by semiconductor photocatalysis, especially if the process is driven by visible light energy. Visible-light active (VLA) photocatalysis, as opposed to traditional energy-intensive and chemically driven disinfection methods such as ozonation, UV irradiation and chlorination, has the potential for achieving high disinfection efficiency with low energy consumption and no harmful by-products. This technology generates in-situ reactive oxygen species (ROS) such as H2O2, and?, without the need for chemicals addition. In turn, ROS are capable of penetrating cell walls and membranes of microorganisms, effectively inactivating them. Although multiple types of VLA photocatalysts have been used experimentally for disinfection of water, noble-metal-based photocatalysts have gained the most interest due to their surface plasma resonance (SPR) effect, which acts synergistically to increase the disinfection potential of the photocatalytic process. This paper is a review of the different types of noble-metal-based VLA photocatalysts used for water disinfection in different experimental settings, their synthesis procedures and disinfection mechanisms. It also discusses innovative approaches to overcome a major hurdle in photocatalysis, that is, the rapid recombination of the electron and hole pair, by including specific dopants into the structure of the photocatalyst.

Single atom doping induced charge-specific distribution of Cu1-TiO_(2) for selective aniline oxidation via a new mechanism

Utilizing single atom sites doping into metal oxides to modulate their intrinsic active sites,achieving precise selectivity control in complex organic reactions,is a highly desirable yet challenging endeavor.Meanwhile,identifying the active site also represents a significant obstacle,primarily due to the intricate electronic environment of single atom site doped metal oxide.Herein,a single atom Cu doped TiO_(2)catalyst(Cu_(1)-TiO_(2)) is prepared via a simple“colloid-acid treatment”strategy,which switches aniline oxidation selectivity of TiO_(2) from azoxybenzene to nitrosobenzene,without using additives or changing solvent,while other metal or nonmetal doped TiO_(2) did not possess.Comprehensive mechanistic investigations and DFT calculations unveil that Ti-O active site is responsible for triggering the aniline to form a new PhNOH intermediate,two PhNOH condense to azoxybenzene over TiO_(2) catalyst.As for Cu_(1)-TiO_(2),the charge-specific distribution between the isolated Cu and TiO_(2) generates unique Cu_(1)-O-Ti hybridization structure with nine catalytic active sites,eight of them make PhNOH take place spontaneous dissociation to produce nitrosobenzene.This work not only unveils a new mechanistic pathway featuring the PhNOH intermediate in aniline oxidation for the first time but also presents a novel approach for constructing single-atom doped metal oxides and exploring their intricate active sites.

Atomically Adjustable Rhodium Catalyst Synthesis with Outstanding Mass Activity via Surface-Li mi ted Cation Exchange

Rh has been widely studied as a catalyst for the promising hydrazine oxidation reaction that can replace oxygen evolution reactions for boosting hydrogen production from hydrazine-containing wastewater.Despite Rh being expensive,only a few studies have examined its electrocatalytic mass activity.Herein,surface-limited cation exchange and electrochemical activation processes are designed to remarkably enhance the mass activity of Rh.Rh atoms were readily replaced at the Ni sites on the surface of NiOOH electrodes by cation exchange,and the resulting RhOOH compounds were activated by the electrochemical reduction process.The cation exchange-derived Rh catalysts exhibited particle sizes not exceeding 2 nm without agglomeration,indicating a decrease in the number of inactive inner Rh atoms.Consequently,an improved mass activity of 30 A mg_(Rh)^(-1)was achieved at 0.4 V versus reversible hydrogen electrode.Furthermore,the two-electrode system employing the same CE-derived Rh electrodes achieved overall hydrazine splitting over 36 h at a stable low voltage.The proposed surface-limited CE process is an effective method for reducing inactive atoms of expensive noble metal catalysts.

Progress in research on catalysts for catalytic oxidation of formaldehyde

Formaldehyde（HCHO）is carcinogenic and teratogenic,and is therefore a serious danger to human health.It also adversely affects air quality.Catalytic oxidation is an efficient technique for removing HCHO.The development of highly efficient and stable catalysts that can completely convert HCHO at low temperatures,even room temperature,is important.Supported Pt and Pd catalysts can completely convert HCHO at room temperature,but their industrial applications are limited because they are expensive.The catalytic activities in HCHO oxidation of transition-metal oxide catalysts such as manganese and cobalt oxides with unusual morphologies are better than those of traditional MnO2,Co3O4,or other metal oxides.This is attributed to their specific structures,high specific surface areas,and other factors such as active phase,reducibility,and amount of surface active oxygens.Such catalysts with various morphologies have great potential and can also be used as catalyst supports.The loading of relatively cheap Ag or Au on transition-metal oxides with special morphologies potentially improves the catalytic activity in HCHO removal at room temperature.The preparation and development of new nanocatalysts with various morphologies and structures is important for HCHO removal.In this paper,research progress on precious-metal and transition-metal oxide catalyst systems for HCHO oxidation is reviewed; topics such as oxidation properties,structure–activity relationships,and factors influencing the catalytic activity and reaction mechanism are discussed.Future prospects and directions for the development of such catalysts are also covered.

Recent developments in metal phosphide and sulfide electrocatalysts for oxygen evolution reaction

Oxygen evolution reaction(OER),as an important half‐reaction involved in water splitting,has been intensely studied since the last century.Transition metal phosphide and sulfide‐based compounds have attracted increasing attention as active OER catalysts due to their excellent physical and chemical characters,and massive efforts have been devoted to improving the phosphide and sulfide‐based materials with better activity and stability in recent years.In this review,the recent progress on phosphide and sulfide‐based OER electrocatalysts in terms of chemical properties,synthetic methodologies,catalytic performances evaluation and improvement strategy is reviewed.The most accepted reaction pathways as well as the thermodynamics and electrochemistry of the OER are firstly introduced in brief,followed by a summary of the recent research and optimization strategy of phosphide and sulfide‐based OER electrocatalysts.Finally,some mechanistic studies of the active phase of phosphide and sulfide‐based compounds are discussed to give insight into the nature of active catalytic sites.It is expected to indicate guidance for further improving the performances of phosphide and sulfide‐based OER electrocatalysts.

Preparation and Microstructural Characterization of Activated Carbon-Metal Oxide Hybrid Catalysts:New Insights into Reaction Paths

In catalysis processes, activated carbon （AC） and metal oxides （MOs） are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and MO nanoparticles in a single hybrid material usually entails both chemical and microstructural changes, which may largely influence the potential catalytic suitability and performance of the resulting product. Here, the prepa- ration of a wide series of AC-MO hybrid catalysts is studied. Three series of such catalysts are prepared by support first of MO （Al2O3, Fe2O3, SnO2, TiO2, WO3, and ZnO） precursors on a granular AC by wet impregnation and oven-drying at 120 ℃, and by subsequent heat treatment at 200 or 850℃ in inert atmosphere. Both the chemical composition and microstructure are mainly investigated by powder X-ray diffraction. Yield and ash content are often strongly dependent on the MO precursor and heat treatment temperature, in particular for the Sn catalysts. With the temperature rise, trends are towards the transformation of metal hydroxides into metal oxides, crystallinity improvement, and occurrence of drastic composition changes, ultimately leading to the formation of metals in elemental state and even metal carbides. Reaction paths during the preparation are explored for various hybrid catalysts and new insights into them are provided.