A Review on Metal-Organic Frameworks as Congenial Heterogeneous Catalysts for Potential Organic Transformations

Metal-organic frameworks (MOFs) have emerged as versatile candidates of interest in heterogeneous catalysis. Recent research and developments with MOFs positively endorse their role as catalysts in generating invaluable organic compounds. To harness the full potential of MOFs in value-added organic transformation, a comprehensive look at how these materials are likely to involve in the catalytic processes is essential. Mainstays of MOFs such as metal nodes, linkers, encapsulation materials, and enveloped structures tend to produce capable catalytic active sites that offer solutions to reduce human efforts in developing new organic reactions. The main advantages of choosing MOFs as reusable catalysts are the flexible and robust skeleton, regular porosity, high pore volume, and accessible synthesis accompanied with cost-effectiveness. As hosts for active metals, sole MOFs, modified MOFs, and MOFs have made remarkable advances as solid catalysts. The extensive exploration of the MOFs possibly led to their fast adoption in fabricating new biological molecules such as pyridines, quinolines, quinazolinones, imines, and their derivatives. This review covers the varied MOFs and their catalytic properties in facilitating the selective formation of the product organic moieties and interprets MOF’s property responsible for their elegant performance.

Photo-Fenton Oxidative System for Removing Tartrazine Yellow Dye in Aqueous Medium Using Y-fe Zeolite As Catalyst

The synthesis and application of heterogeneous solid catalysts in Fenton-type processes have been shown to be a promising alternative for the removal of hazardous pollutants. In this context, the aim of this study was to prepare and characterize a heterogeneous solid iron catalyst supported on zeolite Y for the degradation of yellow food coloring tartrazine (TY). The catalyst was produced through humid ion exchange and characterized by the physisorption of N2, XRD, SEM, TEM and EDX. The efficiency of the catalyst was evaluated through the degradation of tartrazine yellow dye in a batch regime, and the influence of some of the main operational parameters was also evaluated. The characterizations confirmed the presence of iron on the surface of zeolite Y and the increase in the specific area and pore volume after ion exchange. The catalyst used in the photo-Fenton system was extremely efficient, with a removal of approximately 98% in 120 min in the experimental conditions: [TY]0 = 10 mg/L, [H2O2]0 =200 g/L, Y-Fe dosage=1.5 g/L and pH= 3.0. It was possible to recover the catalyst and use it in five reuse cycles, showing its stability and potential application of this catalyst in heterogeneous photo-Fenton systems.

Microwave Assisted Biodiesel Production Using Heterogeneous Catalysts

As a promising renewable fuel, biodiesel has gained worldwide attention to replace fossil-derived mineral diesel due to the threats concerning the depletion of fossil reserves and ecological constraints. Biodiesel production via transesterification involves using homogeneous, heterogeneous and enzymatic catalysts to speed up the reaction. The usage of heterogeneous catalysts over homogeneous catalysts are considered more advantageous and cost-effective. Therefore, several heterogeneous catalysts have been developed from variable sources to make the overall production process economical. After achieving optimum performance of these catalysts and chemical processes, the research has been directed in other perspectives, such as the application of non-conventional methods such as microwave, ultrasonic, plasma heating etc, aiming to enhance the efficiency of the overall process. This mini review is targeted to focus on the research carried out up to this date on microwave-supported heterogeneously catalysed biodiesel production. It discusses the phenomenon of microwave heating, synthesis techniques for heterogeneous catalysts, microwave mediated transesterification reaction using solid catalysts, special thermal effects of microwaves and parametric optimisation under microwave heating. The review shows that using microwave technology on the heterogeneously catalysed transesterification process greatly decreases reaction times (5–60 min) while maintaining or improving catalytic activity (>90%) when compared to traditional heating.

Biodiesel Production from Waste Frying Oils by Potassium Methoxide Supported on Activated Carbon Catalysts from Lignocellulosic Biomass

Various carbon-rich solid catalysts are evaluated for the synthesis of biodiesel from waste frying oil. The study results showed that the use of activated carbon made of corn stalk could increase the biodiesel yield by 7%. The heterogeneous carbon-based catalysts made of lignocellulosic residues could successfully improve the quality of biodiesel properties. The results obtained revealed that the biodiesel properties, including relative density (852–900 kg·m−3) and kinematic viscosity (2.4–3.9 mm2·s−1), are in compliance with the standard limits of ASTM and the European Biodiesel Standard, suggesting that the biodiesel produced would be decent as a diesel fuel that potentially can minimize the serious damage of engine parts, and prolong the engine life.

Facile Synthesis of Iron-Based MOFs MIL-100(Fe) as Heterogeneous Catalyst in Kabachnick Reaction

An effective technique was proposed for the synthesis of novel α-aminophosphonates: a three-component one-pot condensation reaction of aniline, aromatic aldehydes, and triphenyl phosphite in the presence of (MIL-100(Fe)) as a heterogeneous catalyst. Initially, MIL-100(Fe) was synthesized using H3BTC and ferric nitrate at low temperature and atmospheric pressure. Further, MIL-100(Fe) was characterized using various techniques such as XRD, BET surface area, scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR), and thermogravimetric analysis (TGA). Herein, MIL-100(Fe) showed exceptional catalytic performance for the synthesis of α-aminophosphonate and its derivatives compared with conventional solid catalysts, and even homogeneous catalysts. The study demonstrated that MIL-100(Fe) is an ecofriendly and easily recyclable heterogeneous catalyst in Kabachnick reactions for α-aminophosphonate synthesis, with high yield (98%) and turnover frequency (TOF ~ 3.60 min−1) at room temperature and a short reaction time (30 min).