# A New Route for Low Pressure and Temperature
## 1 Introduction  
The widespread industrialization process--i.e., the exponential growth of industrial plants--led to a markedly increase in air, soil, and water contaminants concentration. Economic growth related to industrial development is indeed deeply connected to environmental pollution, and strict standards imposed by new legislation as well as the continuously increasing environmental awareness require practical solutions. Water is a common utility in industrial plants, and the risk of contamination is unavoidably high. An enormous number of organic compounds, widely used in industrial plants (petrochemical, pharmaceutical, bleach, dye, etc. ), are extremely toxic contaminants. In order to meet requirements for discharging or recycling, wastewaters should be adequately treated to deplete concentrations of hazardous molecules. Among them, phenol and its derivatives represent a class of treacherous and high biological dangerous compounds [1; 2; 3], that seriously threaten biological life at high concentrations. Indeed, phenol oxidation follows a complex series of reactions [4; 5; 6; 7], through intermediate compounds increasing potential accumulation. The drawback of the typical phenol reduction processes [8; 9] is that they do not allow a phenol conversion into less dangerous compounds, resulting in a global phenol accumulation. WAO (wet air oxidation) is a well-known method for wastewater treatment, in which highly reactive hydroxyl radical species forming in the reaction environment oxidize organic compounds. However, the process, despite its intrinsic design simplicity, is limited by the prohibitive conditions of pressure, i.e., up to 20 MPa, and temperature, i.e., up to 300 \({}^{\circ}\)C [10; 11; 12]. Heterogeneous catalysis is one of the most effective strategies to improve process efficiency removal [13; 14; 15; 16; 17; 18; 19]. This is particularly true considering the major drawbacks of homogenous catalysis and the problems related to the utilization of biological treatment for highly contaminated wastewater. Many species have been extensively tested as heterogeneous catalysts in catalytic wet air oxidation (CWAO) (e.g., noble metals [20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30], metal oxides [31; 32; 33; 34; 35; 36; 37; 38], carbon materials [39; 40; 41; 42; 43]), in a wide range of conditions, with noble metals showing the highest activity. Among noble metals, platinum and ruthenium have been reported as excellent catalysts towards phenol oxidation. Moreover, a great variety of supports, to disperse and stabilize active phases, and operating at different conditions of temperature (100-160 \({}^{\circ}\)C) and pressure of air (1.5-5.6 MPa), have been investigated for phenol CWAO [20; 21; 26; 28; 29; 35; 36; 39; 44; 45]. Remarkable conclusions can be derived: catalyst poisoning (e.g., sulphur-containing compounds, phosphorous) is a crucial factor ensuring activity; reactions, in particular, high reactants concentration, led to catalyst deactivation due to polymer surface covering; selectivity to CO\({}_{2}\) is influenced by pressure conditions; high temperatures, up to 160 \({}^{\circ}\)C, should be reached in order to enhance reaction rates. Nanotechnology, enabling the perfect control over shape and dimensions of nanocrystals forming in solution, represents a way of innovation for heterogeneous catalysis, with improved diffusions and high surface area exposed (i.e., quasi-homogeneous catalysis). However, the widespread utilization of solid nanoparticles (NPs) in catalysis is limited by aggregation phenomena involving NPs due to the large surface area exhibited in colloidal suspension. Hyper-crosslinked (HCL) polymers can represent an innovative possible solution to this problem, offering the opportunity to embed nanoparticle directly in a porous, chemically stable, polymeric matrix.