Molybdenum trioxide is an abundant natural, low-cost, and environmentally friendly material that has gained considerable attention from many researchers in a variety of high-impact applications. It is an attractive inorganic oxide that has been widely studied because of its layered structure, which results in intercalation ability through tetrahedral/octahedral holes and extension channels and leads to superior charge transfer. Shape-related properties such as high specific capacities, the presence of exposed active sites on the oxygen-rich structure, and its natural tendency to oxygen vacancy that leads to a high ionic conductivity are also attractive to technological applications. Due to its chemistry with multiple valence states, high thermal and chemical stability, high reduction potential, and electrochemical activity, many studies have focused on the development of molybdenum oxide-based systems in the last few years. Thus, this article aims to briefly review the latest advances in technological applications of MoO₃ and MoO₃-based materials in gas sensors, lithium-ion batteries, and water pollution treatment using adsorption and photocatalysis techniques, presenting the most relevant and new information on heterostructures, metal doping, and non-stoichiometric MoO_3−x.

The inadequate discharge of effluents from different sources without prior treatment can impact the characteristics of soil and water, which reflect serious environmental problems. Advanced oxidative processes (AOP) appear as a viable alternative for environmental remediation, including wastewater treatment. Herein, α-MoO₃ and α-Fe₂O₃ semiconductors were synthesized at low temperature by a Pechini-based method and then applied in photocatalysis. The catalytic efficiency was performed under visible light toward the degradation of an organic persistent pollutant (Rhodamine B dye, RhB), commonly present in industries wastewater. The results indicated that the synthesized α-MoO₃ or α-Fe₂O₃ photocatalysts presented a pronounced activity and promoted an efficient RhB degradation after 15 min of reaction. α-MoO₃ had a degradation efficiency of 93% and 98%, while α-Fe₂O₃ showed 67% and 100% RhB degradation without and with the addition of H₂O₂, respectively. These results suggest that the synthesized oxides have high oxi-reductive capacity, which can be used for a fast and effective photodegradation of RhB and other organic persistent pollutants to minimize environmental impacts.

The study aimed to utilize MoO₃ catalysts, produced on a pilot scale via combustion reaction, to produce biodiesel from residual oil. Optimization of the process was conducted using a 2³ experimental design. Structural characterization of the catalysts was performed through X-ray diffraction, fluorescence, Raman spectroscopy, and particle size distribution analyses. At the same time, thermal properties were examined via thermogravimetry and differential thermal analysis. Catalytic performance was assessed following process optimization. α-MoO₃ exhibited a monophasic structure with orthorhombic phase, whereas α/h-MoO₃ showed a biphasic structure. α-MoO₃ had a larger crystallite size and higher crystallinity, with thermal stability observed up to certain temperatures. X-ray fluorescence confirmed molybdenum oxide predominance in the catalysts, with traces of iron oxide. Particle size distribution analyses revealed polymodal distributions attributed to structural differences. Both catalysts demonstrated activity under all conditions tested, with ester conversions ranging from 93% to 99%. The single-phase catalyst had a long life cycle and was reusable for six biodiesel production cycles. The experimental design proved to be predictive and significant, with the type of catalyst being the most influential variable. Optimal conditions included α-MoO₃ catalyst, oil/alcohol ratio of 1/15, and a reaction time of 60 min, resulting in high biodiesel conversion rates and showcasing the viability of MoO₃ catalysts in residual oil biodiesel production.

This study aimed to explore the use of ornamental stone waste as a support for the α-MoO₃ catalyst to develop efficient and sustainable heterogeneous systems for biodiesel production. The catalysts were characterized using physicochemical techniques including X-ray diffraction with Rietveld refinement, FTIR and Raman spectroscopy, scanning electron microscopy with EDS, transmission electron microscopy, nitrogen adsorption/desorption (BET method), particle size distribution, ammonia temperature-programmed desorption (TPD-NH₃), magnetic measurements, and gas chromatography to analyze simultaneous transesterification/esterification (TES) reactions and quantify methyl and ethyl esters. XRD patterns revealed crystalline phases such as mica-biotite, ferro-tschermakite, albite, quartz, and iron-magnesium silicates—components of the catalytic support—as well as orthorhombic α-MoO₃ phases, also confirmed in the heterogeneous systems. FTIR and Raman analyses showed characteristic vibrational bands, while SEM images displayed irregular agglomerates, corroborated by TEM. Nitrogen adsorption isotherms indicated mesoporous structures with surface areas ranging from 0.615 to 3.87 m²/g. Particle size analysis showed D₅₀ values between 5.02 and 20.00 μm, with total acidity ranging from 77.0 to 245 µmol/g of NH₃. Magnetic tests indicated ferrimagnetic behavior. The catalytic performance confirmed the effectiveness of the waste as a support for α-MoO₃, particularly in the system containing 40% Mo ions (40%σ-MoO₃:Waste), which achieved conversions between 78% and 95%. These findings highlight the environmental and technological potential of the studied catalysts, reinforcing the economic viability and ecological relevance of reusing industrial waste in the sustainable production of biodiesel from waste oils.

The search for environmentally correct fuels has been gaining momentum/prominence in scientific research, for example, using oils or fats of animal/vegetable origin and commercial/residual oils. These oils consist primarily of free fatty acids with high energy power and can be converted into fatty acid esters (biodiesel) using highly efficient and recyclable heterogeneous catalysts. Among the heterogeneous catalysts most used in the conversion of biodiesel, two are worth mentioning: MoO₃ and ferrospinels. The first is because it contains in its structure, especially the orthorhombic, acidic active sites of Lewis and Brönsted-Lowry, and the second is because they have high specific surface areas and adequate magnetic characteristics that allow the recovery of the medium. Another interesting point is the use of residues for catalysis that has been highlighted, as they are materials that contain metals such as Fe, K, Si, Mg, Na, and Ti in their composition, which accelerate reactions. Thus, in this sense, this article proposes to carry out a bibliographical survey of the literature in experimental scientific papers and published reviews on the use of MoO₃ and ferrospinels as heterogeneous catalysts supported on waste from cut ornamental rocks (granite/marble) for the production of biodiesel, which is the core of this search, on the online data platforms Science Direct (Elsevier) and Web of Science covering the period from 2016 to April 2023, using the Start software (State of the Art through Systematic Review). The results revealed a quantitative of 223 articles in general, in which 62 were accepted, and 161 were rejected. While in the review extraction stage, 22 papers were accepted, and 40 were rejected. In addition, the review revealed that most of the catalysts and catalytic supports used for the production of biodiesel with oils are oxides, nothing specifically informing the use of waste from cuts of ornamental rocks (granite/marble) as a host material (support) for the catalysts MoO₃ and ferrospinels aiming the production of biodiesel. Therefore, meaning that it is not possible to use this type of residue as a support for catalysts, but rather that there may be a lack of research investigating this application.

The objective of this work was to carry out a literature review of scientific articles published recently on the use of MoO3 and Ni-Zn ferrites as catalysts for biodiesel production, aiming to highlight whether there are studies in the literature reporting the use of MoO3 catalysts supported on Ni ferrite -Zn for biodiesel catalysis applications. The literature review was conducted using the Start software, with a time frame from 2018 to 2023, using the indexed platforms: ScienceDirect, Web of Science and Scopus. As a result, this work showed a wide and consolidated use of ceramic compounds of MoO3 and Ni-Zn ferrites as catalysts in reactions for biodiesel production. The present study also showed a scientific gap in the science of heterogeneous catalysts, since no studies were found that report the use of magnetic catalysts (MoO3/Ni-Zn ferrite), with emphasis on biofuel production.