Morphology evolution and quantitative analysis of β-MoO3 and α-MoO3

Abstract

The morphology evolution from monoclinic molybdenum trioxide (β-MoO3) to orthorhombic molybdenum trioxide (α-MoO3) and quantitative analyses of their mixtures were examined. It was found that the morphology (from spherical to elliptical shape) and color (from green to white) displayed obvious changes when β-MoO3 converted to α-MoO3 in ambient air at 773 K. The transformation from β-MoO3 to α-MoO3 resulted from a change of the internal crystalline structure. The mass percent of β-MoO3 in MoO3 mixtures showed an excellent linear relationship with the relative intensity ratio of the strongest peaks in X-ray diffraction patterns. This approach provides a simple and time-saving method to evaluate the amount of β-MoO3, which is a promising material in catalyst and electrochemical applications, in such mixtures. This finding may provide guidance for the analysis of catalytic performance of MoO3 mixtures. In addition, it was found that β-MoO3 can be easily decomposed into suboxides such as MoO2 and Mo4O11 in pure argon gas atmosphere. The possible decomposition mechanism of β-MoO3 is discussed.

Improved Brønsted to Lewis (B/L) Ratio of Co- and Mo-Impregnated ZSM-5 Catalysts for Palm Oil Conversion to Hydrocarbon-Rich Biofuels

“…On the other hand, the peak at 2θ = 27.6 • in ZSM-5 is sharpened/heightened and shifted to 27.4 • due to the presence of the highest corresponding peak of α-MoO 3 . Wang et al [17] reported that the highest diffraction peak of α-MoO 3 appears at 2θ = 27.36 • ; meanwhile, Sen et al [18] reported that it appears at 2θ = 27.32 [20][21][22][23]. Based on this analysis, it can be deduced that the metals have been impregnated with the ZSM-5 catalyst due to the appearance of the peaks corresponding to the impregnated metals.…”

“…However, these peaks have a higher intensity than those that appear in ZSM-5 catalysts, indicating the peaks of Co 3 O 4 appear and overlap with the corresponding peaks of ZSM-5 at the same Bragg angle. Concerning the Mo/ZSM-5 catalyst, new peaks appear at 2θ = 25.7, 27.4, 33.7, and 38.8 • , corresponding to α-MoO 3 (orthorhombic MoO 3 ) (JCPDS-05-0508) [17][18][19]. It can be seen that the peak at 2θ = 25.7 • in the Mo/ZSM-5 catalyst overlaps with the peak in ZSM-5, in which the peak in Mo/ZSM-5 is higher than in the ZSM-5 catalyst.…”

“…On the other hand, the peak at 2θ = 27.6° in ZSM-5 is sharpened/heightened and shifted to 27.4° due to the presence of the highest corresponding peak of α-MoO3. Wang et al [17] reported that the highest diffraction peak of α-MoO3 appears at 2θ = 27.36°; meanwhile, Sen et al [18] reported that it appears at 2θ = 27.32°. Moreover, new peaks appear at 2θ = 26.5, 27.3, 28.2, 32.2, and 33.8° in the Co-Mo/ZSM-5 catalyst, corresponding to β-CoMoO4 (JCPDS-21-0868) [20][21][22][23].…”

Synthesis of β‐MoO3 whiskers by the thermal evaporation method with flowing oxygen gas

“…To confirm the role of oxygen gas in β-MoO 3 whisker formation, some inlet gases such as argon and nitrogen were used or mixed with oxygen gas, but the collected samples had a high content of impurity due to the decomposition of MoO 3 to form mixed α, β-MoO 3 , and MoO 2 . The experiment in the decomposition of β-MoO 3 was conducted by Wang et al 25 They reported that under ambient air, β-MoO 3 decomposed at 773K to form α-MoO 3 . However, under ambient Ar gas at 773K, β-MoO 3 decomposed into MoO 2 , α-MoO 3 , and Mo 4 O 11 compounds.…”

Plasma-Enhanced Atomic Layer Deposition of Molybdenum Oxide Thin Films at Low Temperatures for Hydrogen Gas Sensing

“…The most prominent oxide is stoichiometric molybdenum trioxide (MoO 3 ), which exhibits different polymorphs, including thermally stable orthorhombic α-MoO 3 , metastable monoclinic β-MoO 3 , and hexagonal h-MoO 3 . Besides the trioxide, many different well-defined suboxides are known, exhibiting oxygen vacancies, which are typically responsible for the versatile properties of the material. − While MoO 3 is a wide band gap semiconductor with a band gap of ∼3 eV, the oxygen deficiency of the suboxides leads to n -type behavior and increased electrical conductivity. ,,− Additionally, n -type MoO x has a very low-lying conduction band and a high work function of ∼6.9 eV, which makes it interesting for a variety of optical and electronic applications. ,,,− The two most common applications of molybdenum oxide, especially in the form of thin films, are hole transporting layers (HTL) in silicon or organic photovoltaic cells (OPV) − and gas sensors. − Both applications have recently gained significant attention due to the intended transformation from fossil fuels as one of the major energy sources toward regenerative energy sources, i.e., solar energy. Besides the improvement of solar cells itself, a proper solution for chemical storage of excess energy is required since energy harvesting with solar cells underlies fluctuations.…”