The aim of the project is the development of new active, selective and stable catalysts for syngas (H2+CO) production by methane tri-reforming (CH4-TR) process, involving greenhouse gases (CH4 and CO2), O2 and H2O. The CH4-TR process, combining in a single catalytic bed the endothermic steam reforming (CH4-SR) and dry reforming (CH4-DR) reactions with the exothermic partial oxidation of methane (CH4-CPO), results energetically efficient, gives less coke deposition and utilizes as a reactant CO2, considered one of the main contributor to greenhouse effects. The new perspective brought to the topic of syngas production deals with the adoption of new catalysts supported on ZrO2 or modified-ZrO2 effective for the CH4-TR process. This proposal constitutes an advancement of the project funded last year addressed to Ni based catalysts suitable for CH4-CPO and CH4-DR as distinct processes. The new Ni-based catalysts will be prepared at various Ni loading (0.5-10.0 wt%) using as supports ZrO2 or ZrO2 modified by the addition of CaO or Y2O3 and will be investigated to assess structure and morphology of modified-ZrO2 supports, Ni particles size, catalysts activation conditions (temperature, atmosphere) and catalysts deactivation with respect to catalytic performances. The characterization of the materials will be performed with several techniques including Atomic Adsorption, XRD and textural analyses, UV-vis, FESEM, Raman, TPR, and operando and in situ FTIR. The catalytic activity will be tested in a flow apparatus at atmospheric pressure in steady state conditions, by changing feed ratio, reaction temperature, contact time and catalyst pre-treatment. The combined analysis of characterization and catalytic results is expected to improve the knowledge of the relationship between composition, structure and catalytic performances to obtain syngas from the CH4-TR reaction.
Natural gas (mainly constituted by CH4) is an attractive feedstock for the synthesis of fuels and chemicals, currently derived from petroleum. The increasing global demand for more environmentally friendly processes and materials is a motivation to look for innovative conversion technologies of natural gas. Among the various technologies, one of the most important is the catalytic conversion of methane to syngas (CO+H2) as building block to produce chemicals and liquid fuels. Methane tri-reforming (CH4-TR) for hydrogen and syngas production is a new important route that combines the utilization of a greenhouse gases as CH4 and CO2, with water steam and oxygen, allowing the use of tail gases emitted from fossil fuel-fired power plants [20]. As CO2 is considered the main contributor to greenhouse effects, one challenge of the CH4-TR process is to decrease gaseous CO2 emission from industrial plants. The new perspective brought to the topic deals with the adoption for industrial applications of new catalytic systems for this promising process. Ni-based catalysts are established systems for all methane reforming reactions, economically preferable to noble metal based catalysts due to the high cost and low abundance of the noble metals. Ni catalysts, however, are susceptible to coking with ensuing loss of activity and selectivity. Recent studies reported that tailoring the preparation method led to catalysts with improved performances dependent on Ni particles size, promoters addition, support structures. In turning feasible the tri-reforming technology, another challenge persists in understanding the reaction mechanisms. The acquired new knowledges will allow to identify catalyst potentialities and limitations suggesting the route to materials improvement.
Since nickel supported systems, mainly based on Al2O3 as support, active for the CH4-TR process suffer from deactivation due to coke deposition and since carbon formation is structure-sensitive [27,28], we intend to use as supports ZrO2 and ZrO2 modified by the addition of basic oxide (Y2O3 or CaO). We expect that this modification produces a decrease in the Ni particle size and an increase in the metal-support interaction, thus improving the catalytic properties of the Ni active component and affecting the catalyst resistance to carbon deposition. As a full understanding of the processes occurring at the nanoscale on the Ni-particles surface or at the particle-support interface is still lacking and needs a deeper investigation, we will focus special attention to the structure and morphology of the support, to the nature and dispersion of Ni active sites and to the Ni-support interaction. We will consider the effects of preparation method, the catalysts activation conditions (temperature, time of stream, pre-activation atmosphere) and the catalyst deactivation correlating all these aspects with catalytic results. The final goal is to understand the key parameters determining the reaction mechanisms and the best catalytic performances.
A wide variety of surface and bulk techniques, currently applied in our research group or in collaboration with other units (Dr. Maria Cristina Campa, CNR - Istituto per lo Studio dei Materiali Nanostrutturati; Dr. Simonetta Tuti, Dipartimento di Scienze, Università Rome Tre; Dr. Igor Luisetto, ENEA- Casaccia) will be useful to characterize new Ni-based supported catalysts. X-ray diffraction (XRD) will be used to study the crystalline phase of the support and the mean particle size of the Ni phase (oxide or metal), to be compared with those obtained by FESEM images. Raman Spectroscopy will throw light on the nature of the support, adsorbates and types of carbonaceous species that can form on the catalyst surface during the catalytic process. TPR will clarify the redox properties of the supported Ni species and H2/O2 titration will evaluate dispersion of the metal particles. Thermogravimetric analyses will quantify carbon deposits. In situ UV-vis spectroscopy will be used to investigate electronic features of the supports and of the oxide precursors. FTIR will give information on dispersion, coordinative unsaturation and redox properties of the supported species and their reactivity with suitable probe-molecules (CO and NO) adopting in situ and operando conditions.