The Emergence of CaO-MgO based Binary Oxides of Alkaline Earth Metals as Cost-effective Solid Base Heterogeneous Catalysts and Sorbents: (A Mini Review)

Abstract

The mono or single oxides of alkaline earth metals such as CaO and MgO are a type of non-toxic and non-corrosive solid-base heterogeneous catalysts. Nevertheless, these mono oxide particles can agglomerate and form larger and less active particles at certain temperatures and reduces their catalytic activity. Therefore, the use of thermally stable CaO-MgO binary oxides is recommended. Further, the possible synergistic interactions between two metal centers provides cooperative catalytic behavior to improve catalytic activity compared to their single oxide counterparts. Therefore, the main theme of this review article is to highlight the ability of reported CaO-MgO based alkaline earth binary oxides as cost-effective and efficient solid-base catalysts in variety of organic transformations and to expand their scope in many other unexplored non-asymmetric organic transformations. Literature survey reveals that CMBOs are highly considerable in optimizing recognized organic transformations such as Transesterification, Knoevenagel/Aldol condensations, Isomerization, Oligomerization, Acetylation, Henry reaction, Alcoholysis, Aza-Michael addition, Cracking of Alkanes, H2-production via steam reforming, Photodegradation of organic pollutants and so forth. The literature survey further visualizes that the surface properties of CMBOs such as Brønsted/ Lewis’s basicity, surface area, particle size, structural diversity, Ca: Mg ratios and synergism between Ca and Mg in CMBOs are very useful to promote them as efficient catalysts compared to their single oxide counterparts (pure CaO and pure MgO). The rightness of proposed mechanisms of abovementioned organic reactions by CMBO catalysts is elicited by this review. Moreover, the precursors for CMBOs are inexpensive, highly abundant and eco-compatible. Apart from the catalytic applications, the suitability of the CMBOs in sorption studies including CO2 uptake, ethanol steam reforming, and heavy metal ion removal is also covered.