**1. Introduction**

Hydrogen (H2) and syngas production technology development has been concentrating most of current efforts toward more efficient and responsible use of fossil carbonaceous feedstocks [1, 2]. Moreover, these technologies can utilize energy more efficiently, supply ultraclean fuels, eliminate pollutant emissions at end-use systems, and significantly reduce greenhouse gases emissions, particularly carbon dioxide (CO2) [2]. H2 and syngas are currently mostly produced by steam reforming, partial oxidation, and autothermic reforming which is also known as oxidative steam reforming [2]. For example, H2 is mainly produced by steam methane reforming (SMR), a process that inherently releases huge amounts of greenhouse gases. The primary energy sources to produce hydrogen are hydrocarbon feedstocks (methane, oil, and coal) with 96% of the supply, while the rest (4%) is attained through water electrolysis [3]. However, in past years, it has been challenging to properly forecast the availability of hydrocarbon feedstocks, which in turn adds to its uncertainty as a main feedstock in the H2 production chain. Therefore, the development of novel techniques aimed to diversify H2 and syngas production presents itself as highly necessary, where the gasification of biomass, for example, poses as a promising effort to significantly compete against fossil feedstocks [4, 5], with a carbon-neutral alternative.

Several applications, processes, and configurations have been developed to thermochemically transform solid fuels into a gaseous fuel through a process called gasification. This process consists on the transformation of solid substances that contain carbon such as biomass, coal, or waste into a combustible gaseous product in the presence of air, water steam (H2O(g)), oxygen (O2), CO2, or a mixture of these gasifying agents. The conversion of these substances occurs at high temperatures (~800°C) and moderated pressures (from atmospheric pressure of up to 70 barg) [6–8]. The conventional gasifiers are classified based on the type of bed and direction of the gas flow [9]; the description of their functioning principles and main features can be extensively found in technical literature [10]. In particular, biomass gasification differs from coal gasification, mainly because biomass is a carbonneutral and sustainable energy source and because biomass is more reactive and features a higher volatile content than coal, which results in a lower gasification temperature. This reduces heat loss, undesired emissions, and material problems associated with high temperatures. Biomass also has a low sulfur content, which results in less SOX emissions, but due to its high alkali contents, like sodium and potassium, slagging and fouling are common problems in biomass gasification equipment [11]. There are several studies regarding solid fuel gasification, such as the results reported by [12–14]. On the other hand, disadvantages of catalytic gasification include increased material costs for the catalyst (often rare metals), as well as diminishing catalyst performance over time. The relative difficulty in reclaiming and recycling the catalyst can also be a disadvantage [8].

In general terms, gasification as a process still requires further optimizations to enhance its energy efficiency by overcoming the main aforementioned challenges, such as tar production and moisture content of the biomass. Although new technologies have been developed as effective ways to utilize even toxic and wet biomass for power generation [15] and conventional techniques have been proven to provide a feasible option to reform solid fuels, there are still limitations on the characteristics of the fuel that restrict the use to certain feedstocks. Fixed bed gasifiers may work with solid fuels containing up to 50% of humidity, while fluidized bed gasifiers can work with solid fuels with up to 60% of humidity in the most advanced developments [16]. The products obtained in the different configurations of gasifier devices are mainly composed of H2, CO, CO2, H2O, N2, heavier hydrocarbons (C2–C6), ashes, tar, oils, and small solid carbon particles, among others. Finally, the main disadvantages of conventional autothermic gasification technology are related to the production of undesired species such as particulate matter, tar, and char. The emissions of these species are highly associated to the operational parameters of the process such as temperature, pressure, time and heating speed, solid fuel particle size, and residence time [17]. For these reasons, researchers have studied the technology of inert porous media (IPM) combustion detecting many important advantages, such as low pollutant emissions, high thermal stability, increased reaction temperature due to its internal heat recirculation, and extended flammability limits, among others [18–21].

The main objective of this chapter is to present the use of IPM technology for achieving high-temperature gasification of solid fuel in a hybrid porous media reactor.
