Stability under reforming conditions

At the fundamental research level, there is a need for in-situ catalyst characterization under reforming conditions in order to understand the nature of active species involved and their stabilities during the reforming reactions. In situ studies to... 

Homy et al. [51,52] used brass wires as a structured packed bed for the oxidative steam reforming of methanol. Their investigations show that the leaching by a basic medium can be carried out simultaneously with a metal doping by impregnation or precipitation. The doping was performed to increase the selectivity of the catalyst and its stability under reaction conditions. 

Disulfide bonds between and within polypeptides stabilize tertiary and quaternary structure. However, disulfide bond formation is nonspecific. Under oxidizing conditions, a given cysteine can form a disulfide bond with the —SH of any accessible cysteinyl residue. By catalyzing disulfide exchange, the rupture of an S— bond and its reformation with a different partner cysteine, protein disulfide isomerase facilitates the formation of disulfide bonds that stabilize their native conformation. 

Ni catalysts u g ZrOj as a unique support that seems crucial to minimize coking under reaction conditions applied for CH4/CO2 reforming. For two successfiiUy developed catalysts, (Pt and Ni on Z1O2) the present contribution outlines the sequence of the elementary steps and the catalytic chemistry of the active metal and the support in order to explain catalysts activity and stability. 

The comparison of catalytic properties was made under identical reaction conditions, among three important candidate catalysts, namely, the Pt/y-Al203, Au/a-Fe203, and Cu Ce, x02 y systems [50], The catalytic tests were performed in the reactant feed containing CO, H2, C02, and HzO — the so-called reformate fuel. The effects of the presence of both C02 and H20 in the reactant feed on the catalytic performance (activity and selectivity) of these catalysts as well as their stability with time under reaction conditions have been studied. The composition of the prepared samples and their BET specific surface areas are presented in Table 7.6. The results obtained with the three catalysts in the presence of 15 vol% COz and of both 15 vol% COz and 10 vol% H20 in the reactant feed (with contact time wcat/v = 0.144 g sec/cm3 and X = 2.5) are shown in Figure 7.12. For comparison, the corresponding curves obtained under the same conditions but without water vapor in the feed are also shown in Figure 7.12. 

The addition of Sn to Raney Ni catalysts also improves the stability and corrosion resistance of the catalyst under aqueous phase reforming conditions. 

In summary, the main goal of the present work is the development of a hydrothermally stable microporous silica membrane with prescribed transport properties. Preferably, these steam stable membranes should have very high permselectivities. Because the permselectivity of a molecular sieving silica membrane will drop to the Knudsen value of the y-alumina supporting membrane when the silica membrane deteriorates under steam reforming conditions, a selectivity of the silica layer higher than the Knudsen selectivity is sufficient. In this way the measurement of the permselectivity is a powerful tool to assess the hydrothermal stability of a supported microporous membrane. 

Specific surface area measurements were performed with the unsupported bulk membrane material before and after SASRA, to obtain information about the stability of (doped) y-alumina under steam-reforming conditions. 

It was tried to make membranes using the specifications obtained in the technical economic evaluation. Of main importance besides the economic considerations was of course the stability of the membrane under steam reforming conditions. To test the stability of the prepared membranes, so-called Simulated Ambient Steam Reforming (SASRA) conditions were used. 

Most commercial steam reforming catalysts contain metaUic Ni supported on an oxide such as AljOj, MgO, and MgAl O. Ni is the catalyst of choice because of its high activity toward C-H bond cleavage and low cost. The oxide supports offer superior mechanical and thermal stability under the reaction conditions [18],... 

As suggested in part C of Scheme 13, the apparent concentration of Ru(rV)-OH species remains constant throughout the oxidation process for which depletion of Ru(V)-oxo species (lmax= 390nm) exhibited pseudo-zero-order kinetics. The depletion in [Ru (edta)(0)] is much slower in the presence of an excess of H2O2 and can be ascribed to the reformation of [Ru (edtaXO)] firom [Ru (edta)(H20)] under such conditions. Moreover, the formation of [Ru edta)(OU)] from the aqua complex is significantly slower than that of [Ru (edta)(0)]. For that reason, the [Ru (edta)(0)] species shows an apparent stability but factually involves redox cycling of Ru between [Ru (edta)(0)] and [Ru (edta)(H20)] . The above results point to the possibility of a catalytic pathway for the oxidation of HOU by [Ru (edta)... 

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