The mechanisms involved in the breakdown of the protective ccides formed on Fe-9%Cr l%Mo have been investigated in both air and high pressure CO 2' The initial research programme was to investigate the microstructural changes which occurred with breakaway oxidation, a new EELS detector being cxi missioned to detenni. ne oxygen and raXbon levels. Oxidation in air was performed at temperatures between 500 and 1000'C. SEM and sane TEN cross sectional work was performed to determine the role of oxygen ingression, but prcblems in sample preparation made examination difficult. With cDcidation in high pressure OD2 the change from protective growth to breakaway is accanpanied by massive oxide growths usually at specimen corners. Microstructural changes also occur, with massive carbide growth acccrnpanying the changes in oxide structure. During oxidation, chemical exchanges between the oxidising gas, the metal and the inner oxide all contribute to the deposition of carbon at the metal/ oxide interface. This process generates internal stresses in the oxide, allowing microcracks to develop this enhancing the inward movement of the 002 and causing more, oxidation and carbon deposition. TEM cross sections were prepared to determine the mode of oxidation and the process by which carbon reaches the interface. In theory, EELS analysis allows identification of light elements Mi and above) but in practice the system proved very sample dependent, working well on thin films but very poorly on thick specimens (carbides). Evidence of the range of EELS mapping facilities are presented together with work on a new particle extraction system

Dry reforming of methane (DRM) is an attractive and promising process for the conversion of methane and carbon dioxide which are the most abundant carbon sources into valuable syngas. The produced syngas, which is a mixture of hydrogen and carbon monoxide, can be used as intermediates in the manufacture of numerous chemicals. To achieve high conversion, DRM reaction is operated at high temperatures (700-900 °C) that can cause major drawbacks of catalyst deactivation by carbon deposition, metal sintering or metal oxidation. Therefore, the primary goal is to develop a metal based catalyst for DRM that can completely suppress carbon formation by designing the catalyst composition. The strategy of this work was to synthesize Ni-based catalysts all of which prepared by homogeneous deposition precipitation method (HDP) to produce nanoparticles with narrow size distribution. In addition, control the reactivity of the metal by finely tuning the bimetallic composition and the reaction conditions in terms of reaction temperature and pressure. The highly endothermic dry reforming of methane proceeds via CH4 decomposition to leave surface carbon species, followed by removal of C with CO2-derived species to give CO. Tuning the reactivity of the active metal towards these reactions during DRM allows in principle the catalyst surface to remain active and clean without carbon deposition for a long-term. The initial attempt was to improve the resistance of Ni catalyst towards carbon deposition, therefore, a series of 5 wt.% bimetallic Ni9Pt1 were supported on various metal oxides (Al2O3, CeO2, and ZrO2). The addition of small amount of noble metal improved the stability of the catalyst compared to their monometallic Ni and Pt catalysts, but still high amount of carbon (> 0.1 wt.%) was formed after 24 h of the reaction. The obtained results showed that the catalytic performance, particle size and amount of deposited carbon depends on the nature of support. Among the tested catalysts, Ni9Pt1/ZrO2 showed high stability with the least carbon amount (0.55 wt.%). On the other hand, mono- and bimetallic Co-Ni/ZrO2 were then prepared following the same synthesis protocol. The ZrO2 support was chosen because of its high thermal stability and absence of mixed oxide formation with the active metals. It was demonstrated that on monometallic Co catalyst, the kinetic analysis showed first-order in CH4 and negative-order in CO2 on the DRM rate. The Co catalyst deactivated without forming carbon deposits. On contrary, on monometallic Ni catalyst, the DRM rate was proportional to CH4 pressure but insensitive to CO2 pressure. The Ni surface provides comparatively higher rates of CH4 decomposition and the resultant DRM than the Co catalyst but leaves some deposited carbon on the catalyst surface. In contrast, the bimetallic CoNi catalyst showed kinetics resembling the Co catalyst, i.e., the first-order with respect to CH4 pressure and the negative-order with respect to CO2 pressure on the DRM rate. Noticeably, the stability of CoNi catalyst was drastically improved over the monometallic counterparts and no deposited carbon was detected after the DRM reaction. The results suggest that for an appropriate Co/Ni ratio, the bimetallic CoNi/ZrO2 catalyst exhibits intermediate reactivity towards CH4 and CO2 between Co and Ni producing negligible carbon deposition by balancing CH4 and CO2 activation.

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