MoO3 ZrO2 Research Articles

Exploring tribological characteristics of ZrN-MoSN composite films fabricated via RF magnetron sputtering: Insights from microstructure and performance analysis

Achieving the stringent demands of sustainable tribological industrial applications poses a significant challenge, particular in optimizing the self-lubricant performance of nitride-based films. This paper tackled this challenge by designing and depositing a series of ZrN-MoSN composite films with varying (Mo + S)/Zr ratios, employing RF magnetron sputtering, aimed to enhance the tribological properties through utilizing the high loading capacity of the ZrN matrix and the exceptional self-lubricating attributes of Mo-S-N additives. After conducting thorough investigations on the microstructure, and tribological properties, the results revealed that the dense columnar structured ZrN-MoSN composite films displayed a polycrystalline composition comprising fcc-ZrN and hcp-MoS2 phases, intertwined with amorphous phases of Mo(SN)x and MoS2(N2). (Mo + S)/Zr ratios below 1.08 exhibited a minor impact on the room temperature (RT) tribological properties, while higher ratios led to degradation on RT average friction coefficient (COF) and wear rate (WR). However, the synergistic effect of ZrN matrix and the tribo-phases of layered MoO3 and hard ZrO2 contributed to the significant enhanced 500 °C tribological properties, particularly with an optimized (Mo + S)/Zr ratio of 0.43.

Effect of NiO, ZrO2 and TiO2 on the formation of glass-ceramic cordierite in the MgO–Al2O3–SiO2–MoO3 system

In glass-ceramic design, the two most crucial factors are composition and microstructure both factors control the ability to form a glass and determines its degree of workability. The composition also determines whether internal or surface nucleation can be achieved. If internal nucleation is desired, as is the case in hot forming glassware, right nucleating agents are melted into the glass as part of the bulk composition. For this reason, this research work focuses on obtaining glass-ceramic cordierite starting from a parent glass of the MgO–Al2O3–SiO2–MoO3 system, using NiO, ZrO2 and TiO2 in a range of 1%Wt to 3%Wt, with the objective of identifying which of the oxides most favors the formation of cordierite. Twelve samples were prepared, which were characterized by thermal gravimetric analysis (TGA), differential thermal scanning analysis (DSC), X-ray diffraction (XRD), Elemental X-ray mapping (SEM), and Infrared spectra using the ATR technique (FT-IR). It was found that NiO is the oxide that most promotes the formation of the cordierite phases, in addition to the use of molybdenum as part of the parent glass, which lowers the crystallization temperature of the crystalline phases obtained. This is determined with the results of phase quantification using the Rietveld method, by XRD, where the samples with NiO add up to a content greater than 90 % of cordierite α and β. And it is supported by the SEM results, where the characteristic hexagonal morphologies of cordierite are identified, the IR characterization results where the bands of the bonds of the phases identified by XRD are identified.

Selection of alkali polymolybdates as fluxes for crystallization of double molybdates of alkali metals, zirconium or hafnium, revisited crystal structures of K2Mo2O7, K2Mo3O10, Rb2Mo3O10 and ionic conductivity of A2Mo2O7 and A2Mo3O10 (A = K, Rb, Cs)

Composition, thermal stability, crystal structure, and flux crystallization features of double molybdates of alkali metals with zirconium or hafnium are considered. The homogeneity ranges and crystal structures of lyonsite-related Li2+4xM1-x (MoO4)3 (M = Zr, Hf) were revised. The alkaline polymolybdates being the decomposition products of the double molybdates are shown to be the optimal fluxes for their crystallization. The areas of the ternary systems A2O–MoO3–ZrO2 (A = Li, Na, K, Rb, Cs) suitable for obtaining crystals of the double molybdates are outlined. The crystal structures of K2Mo2O7, K2Mo3O10 and Rb2Mo3O10 obtained as by-products in runs on crystallization of the double molybdates were refined to update the data of previous works. The electrical conductivity of A2Mo2O7 and A2Mo3O10 (A = K, Rb, Cs) was measured and it was found that its highest values are achieved for Cs2Mo2O7 (σ = 1.2⋅10−4 S/cm at 460 °C). The electrical conductivity in the isostructural series A2Mo3O10 (A = K, Rb, Cs) increases from potassium trimolybdate to cesium trimolybdate and reaches σ = 3.1⋅10−5 S/cm at 460 °C for the latter. As a result, it was suggested that ionic conductivity of these polymolybdates is caused by the transfer of oxide ions. This was confirmed with our calculations of the bond valence based energy (BVE) landscapes for oxygen anions in the structures of A2Mo2O7 and A2Mo3O10 (A = K, Rb, Cs), which show predominantly one-dimensional oxide-ion diffusion along the chains formed of molybdenum-centered polyhedra.

Micro-pyrolyzer screening of hydrodeoxygenation catalysts for efficient conversion of straw-derived pyrolysis vapors

Catalyst screening at micro-scale was performed for atmospheric hydrodeoxygenation (HDO) of fast pyrolysis vapors from biomass (wheat straw). The performance of TiO2-supported Pt and MoO3 catalysts and ZrO2 and TiO2-supported WO3 catalysts was compared to industrial Mo- and NiMo based catalysts. In addition, the HDO activity of an industrial HZSM-5/γ-Al2O3 extrudate promoted by MoO3 was investigated. In comparison with unpromoted acidic catalysts such as HZSM-5/γ-Al2O3, decreased deactivation rates and coke yields were obtained with catalysts that are active in HDO. Mo-based catalysts showed a higher selectivity to aromatics compared to aliphatics, while vapor upgrading with Pt/TiO2 favored aliphatics, thereby achieving the highest effective hydrogen index of the non-condensed vapors amongst the tested catalysts. Bulk WO3 was active for deoxygenation (23 % oxygen removal), albeit to a lesser extent compared to bulk MoO3 (37 % oxygen removal). Compared at the same mass of bulk transition metal oxide, the TiO2-supported WO3 and MoO3 catalysts obtained nearly complete deoxygenation (86–96 % oxygen removal), again with the supported MoO3 being more active than the supported WO3 catalyst.For the production of renewable fuels and/or chemicals from biomass via HDO of pyrolysis vapors the catalyst cost directly influences the economy and sustainability of the process. Therefore, this study further investigated red mud, an abundantly produced industrial waste from aluminum industries, and bog iron as two low-cost transition metal catalysts that are rich in iron. These two catalysts were tested at 4 times higher loading (8 mg) than the high-performing catalysts (2 mg). Under these conditions, an oxygen removal of 51 % and 61 % at vapor carbon yields of 22 wt% C and 14 wt% C were obtained for bog iron and red mud, respectively. Both catalysts showed a high selectivity to monoaromatics and ketones. However, bog iron obtained a higher yield of ketones compared to red mud. In addition, phenolics were converted completely by red mud, indicating a higher activity compared to bog iron.

Enhanced sulfur‐resistant methanation performance over MoO3–ZrO2 catalyst prepared by solution combustion method

Sulfur‐resistant methanation of syngas was studied over MoO3–ZrO2 catalysts at 400°C. The MoO3–ZrO2 solid‐solution catalysts were prepared using the solution combustion method by varying MoO3 content and temperature. The 15MoO3–ZrO2 catalyst achieved the highest methanation performance with CO conversion up to 80% at 400°C. The structure of ZrO2 and dispersed MoO3 species was characterized using X‐ray diffraction and transmission electron microscopy. The energy‐dispersive spectrum of the 15MoO3–ZrO2 catalyst showed that the solution combustion method gave well‐dispersed MoO3 particles on the surface of ZrO2. The structure of the catalysts depends on the Mo surface density. It was observed that in the 15MoO3–ZrO2 catalyst the Mo surface density of 4.2 Mo atoms nm−2 approaches the theoretical monolayer capacity of 5 Mo atoms nm−2. The addition of a small amount of MoO3 to ZrO2 led to higher tetragonal content of ZrO2 along with a reduction of particle size. This leads to an efficient catalyst for the low‐temperature CO methanation process.

Bifunctional Sulfonated MoO3–ZrO2 Binary Oxide Catalysts for the One-Step Synthesis of 2,5-Diformylfuran from Fructose

Sulfonated MoO3–ZrO2 binary oxides (MZS) with different Mo/Zr ratios were synthesized and applied as bifunctional catalysts for the simple one-pot transformation of fructose to 2,5-diformylfuran (DFF). The presence of Bronsted acid sites and the molybdenum oxide species in the catalysts is responsible for the high efficiency and good activity of the catalysts. The former contributes to a high yield of 5-hydroxymethylfurfural (HMF) in the fructose dehydration, and the latter has the role of catalyzing the selective aerobic oxidation of the resulted HMF into DFF. In optimized reaction conditions, DFF yield of 74% with fructose of 100% can be achieved in a one-step reaction. The catalyst can be separated, simply regenerated, and reused without any significant loss in activity, indicating its great potential for the industrial mass production of DFF from fructose.

Efficient production of biodiesel from both esterification and transesterification over supported SO42−–MoO3–ZrO2–Nd2O3/SiO2 catalysts

SO42−–MoO3–ZrO2–Nd2O3/SiO2 (SMZN/SiO2) catalysts for the production of biodiesel via both esterification and transesterification were prepared and characterized by N2 adsorption-desorption isotherms, X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry analysis (TGA), ammonia adsorption Fourier transform infrared spectra (NH3-FTIR), and ammonia adsorption temperature programmed desorption (NH3-TPD) to reveal the dependence of the stable catalytic activity on calcination time. The reason for catalyst deactivation was also studied. The calcination time remarkably affected the types of active centers on SMZN/SiO2, and 4 h was found to be the optimal calcination time. SO42− species bonded with small size ZrO2 were found to be the stable active centers, where the leaching of SO42− and the deposition of coke were inhibited. The deposition of coke was easier on large size ZrO2 than on small size ones. Calcination in air flow could eliminate the deposited coke to recover the deactivated catalysts.

C5–C7 linear alkane hydroisomerization over MoO3–ZrO2 and Pt/MoO3–ZrO2 catalysts

The catalytic activity of MoO3–ZrO2 and Pt/MoO3–ZrO2 has been assessed based on the C5–C7 linear alkane hydroisomerization in a microcatalytic pulse reactor at 323–623K. The introduction of Pt altered the crystallinity and acidity of MoO3–ZrO2. The catalytic activity of Pt/MoO3–ZrO2 was inferior than that of MoO3–ZrO2, although the Pt/MoO3–ZrO2 performed higher hydrogen uptake capacity. IR and ESR studies confirmed the heating of MoO3–ZrO2 in the presence of hydrogen formed active protonic acid sites and electrons which led to change in the Mo oxidation state. Similar phenomenon was observed for Pt/MoO3–ZrO2 at ⩽323K. Contrarily, heating of Pt/MoO3–ZrO2 in the presence of hydrogen at higher temperature did not form protonic acid sites but intensified Lewis acidic sites. It is suggested that Pt facilitates in the interaction of spiltover hydrogen atom and MoO3 to form MoO2 or Mo2O5 over ZrO2 support which may be intensified the Lewis acidic sites.

Physicochemical characterization and catalytic applications of MoO3–ZrO2 composite oxides towards one pot synthesis of amidoalkyl naphthols

A series of MoO3–ZrO2 composite oxide catalysts were prepared by coprecipitation and impregnation methods and characterized by XRD, Raman, UV–Vis, TEM and sorptometric techniques. Characterization studies indicated the presence of tetragonal zirconia phase and well dispersed MoO3 species as isolated and polymolybdate clusters in the composite oxide. The MoO3(20 mol%)–ZrO2 material was used as efficient catalyst for synthesis of amidoalkyl naphthols under solvent free conditions using conventional as well as microwave heating. The results obtained clearly showed that the composite oxide catalyst was recyclable and highly efficient for the reaction giving good yield and purity of the products.

Polycrystalline materials in MoO3–ZrO2–V2O5 system

Melt quenching technique was applied to study tendency for phase formation and amorphization in the MoO3–ZrO2–V2O5 system. By X-ray diffraction were detected the main crystalline phases separated during the quenching: Zr(MoO4)2, V2MoO8, (Mo0.3V0.7)2O5, V0.95Mo0.97O5 but in a wide concentration range the dominant crystalline phase was monoclinic ZrO2. The average particle sizes of the obtained crystal phases were in the range 30–50 nm. A narrow glass formation area was situated, near MoO3–V2O5 side. The glass-crystalline samples were obtained in the MoO3- and V2O5-rich compositions. The phase formation was proven by IR analysis also. IR data showed that the main structural units built up the glass network are corner shared VO5 and MoO6 groups while in the corresponding crystal V2MoO8 phase MeO6 (Me = V, Mo) octahedra are corner and edge shared (band at 580 cm−1).

Water-tolerant catalysis by Mo–Zr mixed oxides calcined at high temperatures

“Water-tolerant catalysis’' of Mo–Zr mixed oxides was investigated using XRD, NH3 temperature-programmed desorption (TPD), adsorption of water and water-concerning reactions such as hydrolysis of ethyl acetate in excess water and esterification of acetic acid with ethanol in a solid–liquid reaction system. It was found that the activities of MoO3–ZrO2 calcined at 1073 K became higher at Mo contents [Mo/(Mo+Zr)] of around 0.2 atomic ratio. When MoO3–ZrO2 was calcined at 873–1073 K, the catalytic activity was greatly enhanced and became comparable to that of H-ZSM-5 (Si/Al=40). Whereas the acid strength of MoO3–ZrO2 measured by NH3-TPD was unaffected by the calcination temperature, the amount of acid and the surface area decreased monotonically as the calcination temperature increased. On the other hand, the surface hydrophobicity estimated from the amount of water adsorbed on the surface was greatly enhanced with increase in the calcination temperature. Therefore, it was concluded that the high activity of MoO3–ZrO2 calcined at high temperatures is predominantly responsible for the enhanced surface hydrophobicity.

Skeletal reactions of hydrocarbons on Pt/WOx-(MoOx-)ZrO2 superacid catalysts

1%Pt/WO3–(MoO3–ZrO2 superacid catalysts (d app of Pt ~16–20 A) gave activity in hydrocarbon isomerization reactions which was much enhanced relative to more customary forms of supported platinum. This is ascribed to dual-functional action. Isomerization selectivity was particularly high for Pt/WOx–ZrO2. The dideuterium/cyclopentane exchange “chemical probe” reaction on identical catalysts (reduction temperature 548 K (10 h)) revealed the action of electron-deficient platinum sites. While there is no clear evidence from hydrocarbon hydrogenolysis activities for such sites, comparison with published literature suggests that the exposure of electron-deficient sites may now be sensitive to the choice of precursor compound used in catalyst preparation.