Molybdenum Species Research Articles

Recovery of molybdenum from alkaline leach solution of spent hydrotreating catalyst by solvent extraction using methyl tricaprylammonium hydroxide

Detailed extraction of molybdenum(VI) from alkaline sodium hydroxide solution by quaternary ammonium salt (Aliquat 336, R3CH3NOH) mixed with kerosene was investigated. The different factors affecting the extraction system such as time of shaking, alkali, extractant, metal ion concentrations, temperature and the organic to aqueous volume phase ratio were studied in order to obtain the best conditions for separating molybdenum(VI). Based on the slope analysis method, the extracted molybdenum(VI) species was suggested to be [(R3CH3N)2MoO4]. Increasing the temperature was found to slightly increase the extraction affinity indicating the endothermic character of the process. Stripping was successfully accomplished by 2.0 M NaOH solution. The extraction procedures were applied to recover molybdenum(VI) from a sample of spent hydrotreating catalyst containing a significant amount of Al(III), Cu(II) and Ni(II). The recovery yield was found to be 96% and a hydrometallurgical flowsheet was also proposed.

Modeling the interaction of molybdenum species adsorbed on a pyrolytic graphite platform and correlations with XPS spectra at different ETAAS stages

Adsorptions of molybdenum species and interactions on a model pyrolytic graphite platform (PGP) sites were calculated employing quantum methods (density functional theory (DFT) and parametric method number 6 (PM6)). The aim of this work is to propose, at the molecular level, the structure of different chemisorbed species on the PGP surface used in the electrothermal atomic absorption spectroscopy (ETAAS) process for a Mo analyte. The carbon surface was modeled by a seven-ring polycyclic aromatic system (coronene). Molybdenum species (Mo, Mo2, MoO, MoO2, MoO3, and MoO4) adsorbed on a coronene surface were studied on different adsorption sites. Calculations of these species showed that chemisorption strengths are stronger on dehydrogenated and decarbonized edge sites than on sites located in the flat central region of the model graphite. It was confirmed that Mo-oxygenated species interactions are very strong at the edge sites and therefore the reduction of these species must occur before the atomization (evaporation of Mo species) takes place, in agreement with experimental results. Comparisons between experimental XPS spectra for ETAAS process (drying, ashing, and atomization) and calculated adsorption energies of Mo species allow an interpretation of which species are present on the PGP at each stage. The presence of very strong bonded molybdenum carbide species on decarbonized sites may explain the memory effects. Experimentally observed migration of Mo oxide species to the edges of the PGP is also corroborated by their small chemisorption energies on central sites of the PGP model.

Influence of incorporating a small amount of silica on the catalytic performance of a MoO3/Al2O3 catalyst in ethanol oxidative dehydrogenation

The influence of incorporating a small amount of silica on the catalytic performance of MoO3/Al2O3 catalyst was studied. Molybdenum supported on pure alumina and 5% SiO2-Al2O3 supports were synthesized. The catalysts were characterized by XRD, Raman, UV-Vis and IR spectroscopies, FE-SEM microscopy, and their activity was evaluated in the oxidative dehydrogenation of ethanol to acetaldehyde. Molybdenum supported on pure alumina gives a 74% yield to acetaldehyde (at 573 K) due to the generation of oxy-dehydrogenation active sites by molybdenum and to the decrement of the alumina dehydration sites. For the molybdenum catalyst supported on silica-containing alumina, the molybdenum species were displaced from the strongest alumina’s acid-base couples, located on nanoparticles edges, corners and defects, to weaker ones located on plane faces causing the rise of weakly bonded species with less active redox behavior.

One-pot synthesis of ZrMo-KIT-6 solid acid catalyst for solvent-free conversion of glycerol to solketal

A series of zirconium and molybdenum species incorporated into ordered mesoporous silicate KIT-6 (ZrMo-KIT-6) materials were designed and synthesized from a one-pot hydrothermal method. The influences of Zr and Mo contents and calcination temperature in ordered mesoporous structure and existing states of introduced Zr and Mo species were systematically researched by SXRD, N2-physisorption, TEM, elemental mapping, TG-DSC, WXRD, Raman, UV and XPS techniques. The results indicated that Zr and Mo species were incorporated into the skeleton of material as designed and existed as a highly dispersed state when the content was below 7%. Also, the ZrMo-KIT-6 material had ordered mesostructure with excellent textural properties, and the ordered mesoporous pores and highly dispersed Zr and Mo species could be preserved even treated at 700 °C. The acidic properties of ZrMo-KIT-6 materials were tested by NH3-TPD and FT-IR spectra of adsorbed pyridine techniques. Owing to the excellent acidic property, the ZrMo-KIT-6 material was employed as a solid acid catalyst for acetalization of glycerol with acetone. The ZrMo-KIT-6(5–700) material showed optimal catalytic performance (conversion of glycerol was 85.8% and selectivity of solketal was 97.8%), and there was no obvious decline in catalytic performance even after five cycles.

Highly active P-doped sulfided NiMo/alumina HDS catalysts from Mo-blue by using saccharose as reducing agents precursor

Saccharose (SA) was used as organic additive in simultaneously impregnated P-doped NiMo/Al2O3 hydrodesulfurization (HDS) catalysts (Mo, Ni and P at 12, 3, and 1.6 wt%, respectively). One-pot impregnating solutions were prepared by MoO3 digestion (∼353 K) in diluted aqueous H3PO4, followed by 2NiCO3·3Ni(OH)2·4H2O addition. Saccharose (SA, SA/Ni = 0.5, 1–3) was dissolved in originally emerald-green impregnating solutions which changed to cobalt blue by room-temperature aging (2–4 days, depending on SA concentration) due to Mo-blue formation by partial molybdenum species reduction. After sulfiding of samples impregnated with SA shorter MoS2 slabs of enhanced stacking were observed (by HR-TEM). Ni and Mo dispersion and nickel sulfidability (as determined by XPS) increased with the amount of organic modifier. Enhanced hydrodesulfurization activity in dibenzothiophene HDS was registered for catalyst obtained from Mo-blue precursor as to that of corresponding materials obtained from conventional emerald-green NiMoP impregnating solutions (with or without SA). However, in solids at high saccharose content (SA/Ni = 3) enhanced “NiMoS” phase amount was not reflected in improved activity. Probably, excessive amount of carbonaceous deposits from SA residua decomposition during catalyst activation provoked partially plugged porous network (as determined by N2 physisorption) in sulfided formulations. That fact seemed to limit accessibility of reactant molecules to surface active sites. Mo-blue precursor obtained through monosaccharides partial reduction seemed to play decisive role in obtaining HDS catalysts of improved properties. Saccharose results a highly soluble, cheap and non-toxic environmentally-friendly additive to produce catalysts of enhanced HDS activity.

An efficient ordered mesoporous molybdate-zirconium oxophosphate solid acid catalyst with homogeneously dispersed active sites: Synthesis, characterization and application

Ordered mesoporous molybdate-zirconium oxophosphate (M-ZrPMo) solid acid catalysts with controllable molybdenum contents (0–20%) are designed and synthesized through a one-pot evaporation-induced self-assembly strategy. Afterwards, ordered mesostructure and molybdenum species in the materials are systematically researched by a variety of means. The results show that M-ZrPMo has highly ordered mesoporous structure with large specific surface area (∼200 m2·g−1), big pore volume (∼0.30 cm3·g−1) and pore size (∼6.5 nm). Additionally, ordered mesoporous structure of M-ZrPMo can be efficiently preserved even treated at 700 °C, presenting an outstanding thermal stability. Meanwhile, the molybdenum species are introduced as designed and homogeneously dispersed in mesoporous framework even at molybdenum content up to 20%. More importantly, the Brønsted and Lewis acidic properties of these materials are successfully enhanced with the introduction of molybdenum species. Meantime, the M-ZrPMo is employed as a solid acid catalyst for alkylation of aromatic compounds and esterification of levulinic acid with 1-butanol. The effect of molybdenum contents and calcination temperature on catalytic performance is thoroughly discussed. The excellent activity and reusability suggested that M-ZrPMo is a promising solid acid catalyst.

Nanostructured molybdenum carbide on biochar for CO2 reforming of CH4

A simple procedure was developed to synthesize molybdenum carbide nanoparticles (Mo2C/BC) by carburization of molybdate salts supported on the biochar from pyrolysis of biomass without using extra carbon source or reducing gas. The molybdenum carbide formation procedure investigated by in-situ XRD and TGA-MS indicated that the phase transitions followed the path of (NH4)6Mo7O24·4H2O → (NH4)2Mo3O10 → (NH4)2Mo14O42 → Mo8O23 → Mo4O11 → MoO2 → Mo2C. The volatile gases CO, H2, and CH4 evolved from biochar and the biochar solid carbon participated in the reduction of molybdenum species, while the biochar and CH4 served as carbon sources for the carburization.Temperature programmed surface reactions of Mo2C/BC indicated that CH4 dissociated as CH4 ⇋ C∗ + 2H2 on the catalyst surface, and CO2 reacted as CO2 + C∗ ⇋ 2CO+ ∗ due to oxidation of Mo2C. Both experiment data and thermodynamic analysis for the study of operation conditions of CO2 reforming of CH4 clearly demonstrated that the yields of H2 and CO increased with the increased temperature and the reasonable conversions should be performed at 850 °C, at which both CH4 and CO2 conversions were higher than 80%.

Enhanced ethylene selectivity and stability of Mo/ZSM5 upon modification with phosphorus in ethane dehydrogenation

Nonoxidative conversion of ethane to ethylene and/or BTX (benzene, toluene, and xylene) suffers rapid deactivation due to coke deposition. We report here the effects of phosphorus modification on the stability and activity of Mo/ZSM5 for nonoxidative conversion of ethane. The results show that the ethylene and BTX yield and stability are significantly enhanced upon modification with 2.5 wt.% P. NH3 TPD, pyridine FTIR, 1H MAS NMR, 27Al MAS NMR, 31P MAS NMR, 129Xe NMR, XPS, UV–visible diffuse reflectance spectra (UV–vis DRS), and nitrogen physisorption were carried out to understand the effects of P on the structure of Mo/ZSM5 and its correlation with catalytic performance. The presence of P reduces the acid strength and density, changes the channel system of ZSM5 by forming thermally stable SAPO-like interfaces with the framework Al, and improves the dispersion of molybdenum. Rapid deactivation still occurs on Mo/ZSM5 with 1 wt.% P due to the existence of denser silanol groups, more isolated Mo species, and reduced aperture size with little change in effective micropore volume. A higher P loading (2.5 wt.%) leads to less dense silanol groups and less reduced but stable molybdenum species, and simultaneously reduces channel diameter and internal volume. Consequently, the ethylene selectivity is enhanced and the formation of coke precursors is restricted, resulting in improved stability.

Effect of zirconia morphology on sulfur-resistant methanation performance of MoO3/ZrO2 catalyst

Two kinds of ZrO2 support with different morphologies were prepared by facile solvothermal method in different solvents. The obtained two supports showed monoclinic zirconia (m-ZrO2) and tetragonal zirconia (t-ZrO2) phase with similar crystalline size. Their supported Mo-based catalysts were prepared by impregnation method and the effect of zirconia morphology on the performance of sulfur-resistant methanation was examined. The results indicated that the MoO3/m-ZrO2 has higher CO conversion than the MoO3/t-ZrO2 catalyst. Characterizations by XRD, Raman, H2-TPR and IR confirmed that the m-ZrO2 is superior to t-ZrO2 for dispersing molybdenum species. In addition, the MoO3/m-ZrO2 catalyst has weaker interaction between support and active Mo speices than the MoO3/t-ZrO2 catalyst, which facilitates to forming active species of nanocrystalline MoS2 layers for sulfur-resistant methanation. The weaker interaction of molybdenum species with m-ZrO2 is related with the more covalent character of the ZrO bond and more oxygen defective structure of m-ZrO2. A larger number of Lewis acid centers appear on the surface of m-ZrO2, which verified the substantial vacancies on m-ZrO2 exposing coordinately unsaturated Zr3+ and Zr4+ cations. Meanwhile, the less Lewis acid of t-ZrO2 result in stronger interaction between support and molybdenum species and trigger crystalline phase MoO3 and MoOZr linkages.

Active Molybdenum-Based Anode for Dehydrogenative Coupling Reactions.

A new and powerful active anode system that can be operated in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) has been discovered. In HFIP the molybdenum anode forms a compact, conductive, and electroactive layer of higher-valent molybdenum species. This system can replace powerful but stoichiometrically required MoV reagents for the dehydrogenative coupling of aryls. This electrolytic reaction is more sustainable and allows the conversion of a broad scope of activated arenes.

Structure evolution of mononuclear tungsten and molybdenum species in the protonation process: Insight from FPMD and DFT calculations

In this work, we apply static density functional theory (DFT) calculations, as well as classical and first-principles molecular dynamics (FPMD) simulations, using the free-energy perturbation method to study the protonation ability, active site and structures of W(VI) and Mo(VI) in acidic aqueous solution. Using FPMD simulations, utilizing the pKa's calculation technique, we concluded that the octahedral WO2(OH)2(H2O)2 is the true formula for tungstic acid (H2WO4), and the hydroxyl ligands are the acidic site. This aqueous structure of H2WO4 is analogous to the previously reported structure of molybdic acid (H2MoO4). The FPMD trajectories of the tungstic acid deprotonation show that the mono-protonated monotungstate ion (HWO4−) may partially exist as a five-coordinated WO3(OH)(H2O)− species except for the four-coordinated WO3(OH)− species. This result is supported by DFT calculations, with an isoenergetic point (ΔE = 1.9 kcal·mol−1) for the WO3(OH)(H2O)− and WO3(OH)− species, when explicit solvent molecules are taken into account. In contrast, for the H2MoO4 acid, FPMD trajectories during the deprotonation process show that two H2O ligands immediately escape from the first coordinated sphere of Mo(VI) to form the four-coordinated MoO3(OH)− species. This difference indicates that structural expansion of W(VI) began in the first protonated step, while that of Mo(VI) only occurs in the second step. In addition, our calculated first and second acid constants for tungstic acid are higher than previously reported values for molybdic acid. This result suggests that WO42− is more easily protonated than the MoO42− anion in the same acidic solution, which is further confirmed by DFT calculations of hydrated oxoanions and its protonated species, based upon the hydration energy.

Speciation Model of the Mo(VI)-Ni(II)-Citrate-S(VI)-N(III) Aqueous System for the Study of the Electrodeposition of Molybdenum and Nickel Oxides Films

A speciation model is proposed for the determination of the concentration of different species formed in an aqueous solution containing Mo(VI), Ni(II), citrate, ammonia and sulfate at 298 K, 105 Pa and variable pH and Mo(VI)/Ni(II) activity ratios. This solution is to be used as electrolyte in the electrodeposition process of thin films of Mo and Ni oxides, which appear to be a promising material for the fabrication of photo-anodes for water splitting in photo-electrochemical cells. The speciation model comprises 53 species and their stability constants, which are related through molar and charge balances to estimate the composition of the solution given a pH value and formal concentrations. As a result, predominance and distribution diagrams are produced, based on which electrolyte conditions (pH and central species concentrations) are recommended to maximize the availability of desired species for the electrodeposition process. Eh-pH diagrams for molybdenum and nickel species at the recommended activities (10−2 for Mo and Ni species, and 10−1 for citrate, ammonia and sulfate species) are also produced, to determine the adequate potential range to be applied for the electrodeposition of Mo and Ni oxides films.

Self-metathesis of 1-butene to ethene and hexene over molybdenum-based heterogeneous catalysts

A novel route involving self-metathesis of 1-butene under mild conditions that gave high yields of ethene and hexene was proposed. The results of thermodynamic analysis revealed that the Gibbs energy of the target Metathesis I reaction (1-butene → ethene + 3-hexene) was much higher than that of the main side Metathesis II (1-butene + 2-butene → propene + 2-pentene). Suppression of 1-butene double-bond isomerization was the key step to increase the selectivity for the target olefin in the reaction network. The relationship between the catalytic performance and support nature was investigated in detail. On basis of H2-TPR, UV-Vis spectra and HRTEM results, an alumina (Al2O3) support with large surface area was beneficial for the dispersion of molybdenum (Mo) species. Both suitable acidity and sufficient Mo dispersion were important to selectively promote the self-metathesis reaction of 1-butene. On the optimal 6Mo/Al2O3 catalyst, 1-butene conversion reached 47% and ethene selectivity was as high as 42% on the premise of good catalytic stability (80 °C, 1.0 MPa, 3 h−1).

Influence of pH of Nitric Acid Solution on the Kinetics of the 99Мо Sorption onto Titanium Hydroxide

The kinetics of the 99Мо sorption onto T-5 sorbent at different pH values of the nitric acid solution was studied. The previously suggested limiting steps of the 99Мо sorption onto Т-5 sorbent were confirmed. The effective rate constant of the molybdenum sorption onto titanium hydroxide (fast step) as a function of pH passes through a maximum at pH from 4.5 to 5.5, which does not correspond to the maximum of the pH dependence of the distribution coefficient but correlates with the maximal content of one of the sorbable species, НМоО4–, in the solution. Thus, the rate of Mo sorption onto titanium hydroxide as a function of pH passes through a maximum at a minimal negative charge of the sorbate near pH of the isoelectric point of the sorbent. The kinetic studies confirm the scheme of the sorption of molybdenum hydroxo complexes onto titanium hydroxide, suggested previously on the basis of the logkd–рН and log e–log[m] sorption isotherms. According to this scheme, simultaneous redistribution and sorption of sorbable molybdenum species, МоО2ОН+, Н2МоО4, and НМоО4–, are possible.

Regioselective Termination Reagents for Ring-Opening Alkyne Metathesis Polymerization.

Alkyne cross-metathesis of molybdenum carbyne complex [TolC≡Mo(OCCH3(CF3)2)3]·DME with 2 equiv of functional ynamines or ynamides yields the primary cross-metathesis product with high regioselectivity (>98%) along with a molybdenum metallacyclobutadiene complex. NMR and X-ray crystal structure analysis reveals that ynamides derived from 1-(phenylethynyl)pyrrolidin-2-one selectively cleave the propagating molybdenum species in the ring-opening alkyne metathesis polymerization (ROAMP) of ring-strained 3,8-dihexyloxy-5,6-dihydro-11,12-didehydrodibenzo[a,e][8]annulene and irreversibly deactivate the diamagnetic molybdenum metallacyclobutadiene complex through a multidentate chelate binding mode. The chain termination of living ROAMP with substituted ethynylpyrrolidin-2-ones selectively transfers a functional end-group to the polymer chain, giving access to telechelic polymers. This regioselective carbyne transfer strategy gives access to amphiphilic block copolymers through synthetic cascades of ROAMP followed by ring-opening polymerization of strained ε-caprolactone.

Maize Stalk as Natural Ion Exchanger for Hazardous Pollutants

This paper recommends maize stalk as a cheap natural ion exchanger. Ion exchange equilibrium was studied using thermodynamic and kinetic models. The results showed a high selectivity towards cationic species of antimony (III), molybdenum (VI), lead (II) and arsenium (III). Waste waters and sediments from tailing ponds samples were analysed.

Monomeric and Dimeric Oxidomolybdenum(V and VI) Complexes, Cytotoxicity, and DNA Interaction Studies: Molybdenum Assisted C═N Bond Cleavage of Salophen Ligands.

Four novel dimeric bis-μ-imido bridged metal-metal bonded oxidomolybdenum(V) complexes [MoV2O2L'21-4] (1-4) (where L'1-4 are rearranged ligands formed in situ from H2L1-4) and a new mononuclear dioxidomolybdenum(VI) complex [MoVIO2L5] (5) synthesized from salen type N2O2 ligands are reported. This rare series of imido-bridged complexes (1-4) have been furnished from rearranged H3L'1-4 ligands, containing an aromatic diimine (o-phenylenediamine) "linker", where Mo assisted hydrolysis followed by -C═N bond cleavage of one of the arms of the ligand H2L1-4 took place. A monomeric molybdenum(V) intermediate species [MoVO(HL'1-4)(OEt)] (Id1-4) was generated in situ. The concomitant deprotonation and dimerization of two molybdenum(V) intermediate species (Id1-4) ultimately resulted in the formation of a bis-μ-imido bridge between the two molybdenum centers of [MoV2O2L'21-4] (1-4). The mechanism of formation of 1-4 has been discussed, and one of the rare intermediate monomeric molybdenum(V) species Id4 has been isolated in the solid state and characterized. The monomeric dioxidomolybdenum(VI) complex [MoVIO2L5] (5) was prepared from the ligand H2L5 where the aromatic "linker" was replaced by an aliphatic diimine (1,2-diaminopropane). All the ligands and complexes have been characterized by elemental analysis, IR, UV-vis spectroscopy, NMR, ESI-MS, and cyclic voltammetry, and the structural features of 1, 2, 4, and 5 have been solved by X-ray crystallography. The DNA binding and cleavage activity of 1-5 have been explored. The complexes interact with CT-DNA by the groove binding mode, and the binding constants range between 103 and 104 M-1. Fairly good photoinduced cleavage of pUC19 supercoiled plasmid DNA was exhibited by all the complexes, with 4 showing the most promising photoinduced DNA cleavage activity of ∼93%. Moreover, in vitro cytotoxic activity of all the complexes was evaluated by MTT assay, which reveals that the complexes induce cell death in MCF-7 (human breast adenocarcinoma) and HCT-15 (colon cancer) cell lines.

Application of Magnetic Resonance Imaging and Raman Imaging to study the impact of phosphorus in impregnation of hydrotreatment catalysts

Magnetic Resonance Imaging is applied, for the first time, to monitor in-situ the impregnation step of hydrotreatment catalysts with an aqueous solution composed simultaneously of molybdenum, cobalt and phosphorus. This technique provides information about spatial distribution of all metal precursors inside the catalyst pellet with a significantly improved spatial resolution of 39μm×39μm compared to the literature. Streamline Raman Imaging yields complementary information about molybdenum speciation at equilibrium. For a molybdenum based catalyst, a slow transport of molybdenum complexes through γ-alumina is observed by Magnetic Resonance Imaging, which suggests a strong interaction between metal precursor and the support. Presence of polymeric molybdenum ions is found near the edges as well as the formation of an Anderson-type heteropolyanion. In the presence of phosphorus, interaction between molybdenum and γ-alumina is weaken since a preferential adsorption to phopshorus is observed. This phenomenon results in an increase in the transport rate of molybdenum complexes. When phosphorus is added to a molybdenum based catalysts promoted by cobalt, preferential interactions between metal promotor and the support are observed rather than with molybdenum species. This innovative Magnetic Resonance Imaging −Streamline Raman Imaging methodology allows a better control of the deposition process during impregnation and to identify the descriptors that most influence this preparation step. Finally, this methodology can be applied to other type of supported catalysts.

Incorporation of molybdenum into Pd and Pt catalysts supported on commercial silica for hydrodeoxygenation reaction of dibenzofuran

Molybdenum was incorporated into catalysts based on noble metals (Pt or Pd) and supported on silica in order to evaluate how its presence can modify the catalytic response of monometallic catalysts for hydrodeoxygenation (HDO). To this end, the catalysts were evaluated in the hydrodeoxygenation (HDO) reaction of dibenzofuran (DBF) and characterized by different experimental techniques to understand its structure, texture and acidic properties. Catalytic results showed that the active phase had much influence on the activity and selectivity to different reaction products, although, in all cases, bicyclohexane (BCH) was the main reaction product observed. Molybdenum played a very important role in the case of bimetallic catalysts, mainly in the case of palladium. Molybdenum species improved the selectivity to O-free products related to its capacity to break the CO bond. However, molybdenum activity was nil in the absence of noble metal. Moreover, regardless of the noble metal employed, the reducibility, acidity and dispersion of the molybdenum species changed and this is possibly associated to a synergism effect between noble metal and Mo.

Relationship between the catalytic activity and Mo–V surface species in bimetallic catalysts for the oxidative desulfurization of dibenzothiophenic compounds

This work shows the performance of MoOx–VOx based bimetallic catalysts tested on the oxidative desulfurization (ODS) process of refractory dibenzothiophenic compounds using H2O2 as an oxidant. The catalytic activity was related with the oxidation state of molybdenum and vanadium surface species and with the interaction of both metals. The prepared molybdenum–vanadium oxides supported on alumina were subjected to reduction treatments at different temperature to obtain molybdenum and vanadium species with different oxidation state. Catalysts were characterized by their textural properties, scanning electron microscopy–energy dispersive X-ray, X-ray diffraction, temperature programed reduction and X-ray photoelectron spectroscopy. The characterization results showed that metal interactions promote the generation of highly active tetrahedral molybdenum species and isolated vanadium species, which increase the ODS performance of Mo–V based catalysts compared with their respective monometallic catalysts. Also, it was observed that combination of Mo6+, Mo4+ and V4+ superficial species promoted the ODS catalytic activity.