Diploma Thesis Defense by Mrs. Christina Papazaharia

Thesis Title:   «DRY REFORMING OF BIOGAS IN BIMETALLIC AND MONOMETALLIC CATALYST BASED ON Ni-Ir AND Ni

Thursday 8 October 2020, at: 12:30, Venue: https://tuc-gr.zoom.us/j/87539298705?pwd=RHltZEwzQ2FpWEtZN1FoNzk5MmtMdz09

Examination Committee

• Professor            Ioannis V. Yentekakis (advisor)
• Assistant Professor  Nikolaos Xekoukoulotakis
• Assistant Professor Paraskevi Panagiotopoulou

Abstract

This diploma thesis examines the catalytic behaviour of the nickel-iridium bimetallic catalyst (Ni-Ir) and the monometallic nickel catalyst (Ni), as well as the influence of the supported carriers related to alumina, alumina- ceria-zirconia and ceria-zirconia during the process of biogas dry-reforming (DRM). More specifically, the process of the dry reforming of biogas concerns the reaction of carbon dioxide CO2 and methane CH4 with the production of hydrogen H2 and carbon monoxide CO products. This process has gained a great environmental and industrial advantage for two very important reasons. Initially, through this process, the two gaseous pollutants are exploited, and in particular CO2 and CH4, two gases which are considered to be important in the contribution of the greenhouse effect. Also,  CO2 and CH4 are the main components of biogas and natural gas which are relatively inexpensive raw materials for the production of syngas, i.e. synthesis gas H2CO and its subsequent use as fuel in various applications. This is particularly important, since H2 is now considered to be the fuel of the future for the production of electricity.

Subsequently, for the experimental procedure for the study of the reaction, the composition of the selected reactants is equomolecular CO2CH4=11. As regards the content of the catalysts in active metals, for the bimetallic catalyst Ni-Ir the content is1 % w.t Ir-10 % w.t Ni, while for the monometallic catalyst Ni is 1 % w.t Ni. These catalysts are supported in three different carriers. Apart from widely commonly used alumina γ-Al2O3, mixed oxide and more specific ceria CeO2 and zirconium ZrO2 - CZ  and a combination of these two with alumina (ACZ) will be studied. More generally, the role of the carriers/supports is quite significant in terms of enhancing catalytic activity and limiting carbon deposits and especially during dry reformιing of methane processes. In particular, the effects on the activity of the catalytic Ni-Ir and Ni from the carriers, are examined through the study of the stability of the catalysts for a temperature constant at T=750 ℃, as well as their performance behaviour for a range of temperatures. In addition, the influence of other parameters during the operation of the catalysts, which is the reduction and the successive oxidation that are susceptible, in which the resistance and the performance of the catalysts are studied, is examined.

From the results obtained, both nickel Ni catalysts and nickel-iridium bimetallic catalysts Ni-Ir which are examined, they appear to have no tendency to accumulate carbon deposits on their surface, which is the main reason for their deactivation in the hydrocarbon reformation. Additional interest is presented around the studied catalysts in terms of the stability that they lend after the oxidation-reduction changes that are susceptible. Also with regard to their performance at high temperatures, it was noted that the catalysts Ni and Ni-Ir which are based on the body of alumina γ-Al2O3, are more active. Lower yields are presented by the catalysts of Ni-Ir and Ni, relying on the carriers of aluminas- cerium-zirconium (ACZ) and cerium-zirconium (CZ) respectively.