## 1 Introduction  
The global pandemic situation declared in 2020 due to the disease called COVID-19 and government measures to avoid its spread caused a dramatic increase in the consumption of face masks, gloves, and other single-use plastic-based personal protective equipment (PPE) [1]. As a result of the high demand and elevated consumption of these single-use plastic-based materials, a great amount of waste is produced, with a monthly estimation of 129 billion face masks and 65 billion gloves globally [2; 3]. Spain was among the countries with the strictest national lockdown measures in the European Union (EU) during the first wave of the pandemic. After that, the different autonomous communities applied different restriction regimes. The use of masks was encouraged in public spaces and, in some instances, was imposed in public transport. Therefore, in Spain, the COVID-19 pandemic had a noticeable effect on the manufacturing of personal protective products by the Spanish manufacturing industry, due to the strong demand of them by the population. Thus, in 2020, more than 293 million masks were sold. About 265.4 million surgical masks, 27.6 million masks with filtering polymeric fibrous materials (FPP filters), almost 8 million protection screens, and 85,545 tons of hand sanitizer gels were sold. The values of these sales were EUR 149 million in masks, EUR 18 million in screens, and EUR 296 million in gels [4]. As a consequence, the development and application of appropriate eco-friendly methods of management of PPE waste is especially valuable [5]. PPE is made of different types of polymers; even the same equipment has several types of plastic in its structure. For example, surgical masks are usually made of three layers of polypropylene, with nylon ear straps and a metal nose clip wrapped in polyethylene [6]. This factor, coupled with the possible presence of micro-organisms, causes this class of waste requires special treatment [7]. Incineration is currently one of the most widespread methods for the treatment of healthcare waste. However, the combustion gases not only discharge greenhouse gas emissions into the environment but can also release toxic substances, such as dioxins and furans, that need to be properly treated, or particulate matter [8; 9]. Landfilling is another of the most common approaches extensively applied to discard PPE. Nevertheless, there are some important drawbacks to this method. First, since the PPE degrades slowly, the generated toxic substances stay in the air/water/soil for an extended period [10]. Furthermore, landfilling needs a massive space. Therefore, to address the challenges in PPE waste management, different researchers are now working on advanced technologies, such as glycolysis, hydrogenation, hydrolysis, pyrolysis, and gasification to transform PPE into value-added products [11]. Of these approaches, pyrolysis is one of the best techniques for the valorization of PPE due to its high economic viability and technical feasibility [12]. This technique has been commercially used for plastic upcycling by some petrochemical companies worldwide [13]. It consists of the use of thermal energy in an oxygen-free environment to break the chemical bonds of plastic polymers to obtain three valuable products: biooil, syngas, and biochar, which can play an essential role in industries and refineries [9; 14; 15]. The yield and properties of products is strongly influenced by various operating parameters including temperature, heating rate, or usage or not of catalysts, among others. To upgrade the primary products obtained from pyrolysis of plastic waste, different catalysts have been explored. In particular, the effect of several types of zeolite catalysts on the yields of biochar, biooils, and gases has been extensively investigated [16]. Other works includes the use of different metal oxides (Al\({}_{2}\)O\({}_{3}\), Fe\({}_{2}\)O\({}_{3}\), CeO\({}_{2}\), MoO\({}_{3}\), TiO\({}_{2}\), etc.) as catalyst [17; 18].