One of the most crucial attributes of synthetic organic chemistry is to design organic reactions under the facets of green chemistry for the sustainable production of chemicals. Thus, due to the intensified environmental and safety concern, the need for new technologies for conducting chemical transformation has grown. In this regard, there is enormous interest in the use of heterogeneous catalysts as they generally avoid the generation of waste, require fewer toxic reagents, as well as entail easier separation and recycling of the catalyst. α,β-Unsaturated acids have been widely used in various industrial applications and have been identified as one of the most promising chemicals obtained via the Knoevenagel condensation reaction. This review aims to discuss the most pertinent heterogeneous catalytic systems such as zeolites, mesoporous silica, ionic liquids, metal oxides, and graphitic carbon nitride-based catalysts in the Knoevenagel reaction. Ultimately, this review focuses not only on the catalyst but also provides an overall idea and guide for the preparation of new catalysts with outstanding properties by looking at the chemical and engineering aspects such as the reaction conditions and the mechanisms.

Copper oxide and Zinc (Zn)-doped Copper oxide nanostructures (CuO-NSs) are successfully synthesized by using a hydrothermal technique. The as-obtained pure and Zn-doped CuO-NSs were tested to study the effect of doping in CuO on structural, optical, and antibacterial properties. The band gap of the nanostructures is calculated by using the Tauc plot. Our results have shown that the band gap of CuO reduces with the addition of Zinc. Optimization of processing conditions and concentration of precursors leads to the formation of pine needles and sea urchin-like nanostructures. The antibacterial properties of obtained Zn-doped CuO-NSs are observed against Gram-negative (Pseudomonas aeruginosa, Klebsiella pneumonia, Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria via the agar well diffusion method. Zn doped s are found to have more effective bacterial resistance than pure CuO. The improved antibacterial activity is attributed to the reactive oxygen species (ROS) generation.

Catalytic conversion of CO₂ into methane is an attractive method because it can alleviate global warming and provide a solution for the energy depletion crisis. Nickel-based catalysts were commonly employed in such conversions due to their high performance over cost ratio. However, the major challenges are that Ni tends to agglomerate and cause carbon deposition during the high-temperature reaction. In the past decades, extensive works have been carried out to design and synthesize more active nickel-based catalysts to achieve high CO₂ conversion and CH₄ selectivity. This review critically discusses the recent application of Ni-based catalyst for CO₂ methanation, including the progress on the effect of supporting material, promoters, and catalyst composition. The thermodynamics, kinetics, and mechanism of CO₂ methanation are also briefly addressed.