Developing of catalysts for hydrogen production by reforming processes from renewable fuels

Sustainable development depends directly on the availability of sufficient energy resources, consumption over restoration ratios and effects of energy on the environment. Rapid industrialization and modernization has amplified energy demands, exacerbating critical social issues like global warming and climate change, due to the use of fossil fuels for energy supply. Then, progressing toward a more sustainable use of energy resources essentially requires the share of renewable sources into the energy pool, with the exploitation of new different options for energy vectors which can guarantee a high energy density and easy long-term storage. Consequently, the production system, initially fossilbased, evolves toward renewable resources in the long run, contributing to drive the global energy system to a sustainable trajectory. In this context, the biogas is an attractive renewable carbon source and its exploitation would be advantageous from both financial and environmental points of view. An alternative and sustainable use of biogas, respect the conventional uses (ICE, micro-turbine), is based on syngas production, by reforming processes, as a raw material for the production of synthetic fuels with low environmental impact (hydrogen, methanol, dimethylether and synthetic gasolines) via Gas To Liquid (GTL) routes or for the directly utilization in high temperature fuel cell (Solid Oxide Fuel Cell, SOFC) to produce energy and heat. Central issues of reforming processes are the development of efficient, stable and low cost catalysts and compact and lightweight fuel processor. The doctoral thesis is focused on the following features: preparation (by low cost Solution Combustion Synthesis, (SCS), characterization and testing of catalysts in pellets and structured form for biogas Tri-reforming (TR) process. Identification of the correlation between the most important parameters that affect the SCS (fuels and precursors) and the properties of the resulting powders (crystalline or amorphous structure, crystallite size, purity, specific surface area and particle agglomeration, catalytic activity). Utilization the SCS for the preparation of structured catalysts based on cordierite monoliths and foams. Identification of the optimum operating conditions for Tri-Reforming processes especially at high space velocity. Chapter 1 regards biogas production and its composition. Informations on conventional and alternative use of biogas are also reported. Finally, a thermodynamic analysis and a description of the biogas reforming processes is reported. Chapter 2 describes the adopted synthesis method in detail as well as the micro-scale plant and the methods and equipments used for the catalysts characterizations. In chapter 3, the performances of Ni catalysts supported on La−Ce−O, prepared by combustion synthesis, were studied for the tri-reforming of simulated biogas mixture to syngas production. The structure of the catalysts and the effects on the catalysts' performances of the O2/CH4 ratio and the nickel content were investigated in order to identify the optimal operating conditions able to ensure high CH4 and CO2 conversions with elevated H2 yield. Chapter 4 is dedicated to the study of the synthesis method. The influence of fuel (oxalyldihydrazide, urea, carbohydrazide), cerium precursor (cerium nitrate and ammonium cerium nitrate) on the nature of combustion and its correlation with the powder characteristics have been addressed. The prepared catalysts have been characterized, highlighting the effect of the selected preparation variables on the morphological and structural properties and, consequently, on their catalytic activity towards the TR of biogas. Chapter 5 refers to the possibility to use precipitation dry-impregnation method or solution combustion synthesis for the preparation of structured catalysts based on cordierite monoliths (500 cpsi, diameter 1 cm, length 1.5 cm) in which Ni/CeO2 (metals load equal to 7.5 wt.%) catalyst was deposited by support dip-coating into acid-free stable catalyst dispersion. The activity has been focused on the preparation and characterization of structured catalysts, Ni supported on CeO2, coated on cordierite monoliths. A correlation between the chemical-physical properties of the catalytic layers, the characteristics of the final coated samples and the catalytic performances of the structured materials under the biogas Steam Reforming (SR) and Tri-Reforming (TR) condition, were investigated and compared.