# Recovery/Reuse of Heterogeneous Supported Spent Catalysts
###### Abstract  
The rapid separation and efficient recycling of catalysts after a catalytic reaction are considered important requirements along with the high catalytic performances. In this view, although heterogeneous catalysis is generally less efficient if compared to the homogeneous type, it is generally preferred since it benefits from the easy recovery of the catalyst. Recycling of heterogeneous catalysts using traditional methods of separation such as extraction, filtration, vacuum distillation, or centrifugation is tedious and time-consuming. They are uneconomic processes and, hence, they cannot be carried out in the industrial scale. For these limitations, today, the research is devoted to the development of new methods that allow a good separation and recycling of catalysts. The separation process should follow a procedure economically and technically feasible with a minimal loss of the solid catalyst. The aim of this work is to provide an overview about the current trends in the methods of separation/recycling used in the heterogeneous catalysis.  
catalysis; heterogeneous catalysts; separation methods; recycling; recovery +
Footnote †: journal: _catalysis_  
0000-0002-0001-5999-22000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-00000-00000-00000-00000-00000-00000-00000-00000-0000  
Conventionally, catalysts have been categorized as homogeneous and heterogeneous. Homogenous catalysts exhibit advantages in terms of activity and stability due to their good solubility in reaction media. However, homogeneous catalysts are difficult to separate and recover from the reaction mixture, resulting in increasing economic cost, environmental pollution, and corrosion [23]. This problem limits their applications in industry, especially in the drug and pharmaceutical industry owing to the issue of metal contamination in the case of metal-catalyzed synthesis [24]. Although _heterogeneous catalysis_ is generally less efficient compared to the homogeneous counterpart, it benefits from easy recovery. In gas/solid systems, the catalyst is easily separated and cleaned, and, in liquid/solid systems, it can be simply filtered [25]. The bridge between heterogeneous and homogeneous catalytic processes can be achieved through the use of magnetic nanoparticles. Magnetic nanoparticles can operate as catalytic supports enabling immobilization and magnetic recovery of homogenous catalysts [26]. Today, magnetic separation is considered a more competitive technology for the recovery of heterogeneous supported catalysts than traditional methods since it is fast, efficient, consumes low energy, and minimizes the use of solvents and the generation of secondary wastes [27].  
Spent catalysts, once they have completed their useful life, represent a threat to the environment due to the leachable metals from their surface; a way to make their overall process of disposal less toxic to the environment is considering them a secondary source of metals.  
Therefore, nowadays, the development of eco-friendly and highly efficient recovery techniques has become a focus of interest for both academia and industry. Tetronics' DC Plasma Arc technology seems to be the option that best meets these needs.