Catalyst down-selection

A good catalyst is also stable. It must not deactivate at the high temperature levels (1300 to 1400°F) experienced in regenerators. It must also be resistant to contamination. While all catalysts are subject to contamination by certain metals, such as nickel, vanadium, and iron in extremely minute amounts, some are affected much more than others. While metal contaminants deactivate the catalyst slightly, this is not serious. The really important effect of the metals is that they destroy a catalyst s selectivity. The hydrogen and coke yields go up very rapidly, and the gasoline yield goes down. While Zeolite catalysts are not as sensitive to metals as 3A catalysts, they are more sensitive to the carbon level on the catalyst than 3A. Since all commercial catalysts are contaminated to some extent, it has been necessary to set up a measure that will reflect just how badly they are contaminated. 

Separation of the individual contributors can provide useful information about performance optimization for fuel cells, helping to optimize MEA components, including catalyst layers (e.g., catalyst loading, Nafion content, and PTFE content), gas diffusion layers, and membranes. It assists in the down-selection of catalysts, composite structure, and MEA fabrication methods. It also helps in selecting the most appropriate operating conditions, including humidification, temperature, back-pressure, and reactant flow rates. 

Preparation of the Working Electrodes for Catalyst/Catalyst Layer Studies In fuel cell catalyst/catalyst layer down-selection, the process of preparing the working electrodes includes several steps ... 

The results also suggest that through AC impedance measurements, the performance drops caused by individual processes such as electrode kinetic resistance, membrane resistance, and mass transfer resistance can be correlated to either reduction or improvement in cell performance. If individual impedances are known, the contribution to the change in performance can be identified, which is very important in the design and optimization of high-temperature MEA catalyst layer components, structure down-selection, and MEA architecture. 

Phase 2 Laboratory-scale catalyst-coated membranes (CCMs) will be fabricated, optimized and tested using the Phase 1 down-selected membranes and catalysts. 

Phase 3 Full-size CCMs with the down-selected and optimized HTMs and catalysts will be fabricated and tested in two individual multi-cell stacks. 

In the exploring catalysts for fuel cell cathode ORR, besides new catalyst synthesis, catalyst characterization using electrochemical measurements such as RDE and RRDE techniques seems necessary in order to validate the catalytic ORR activity of the synthesized catalysts, and the down-selection of new catalyst designs. 

Early reports on the use of Pt alloys as ORR catalysts for PEM fuel cells were published by a group of scientists at Texas A M University in the early 1990s [4-6]. They created a series of Pt alloys, including Pt-Ni, Pt-Co, Pt-Cr, Pt-Mn, and Pt-Fe, at high temperature (900 °C) under an inert atmosphere. These alloys can be expressed as Pt-M (where M is the non-noble metal alloying component). In the process of activity down-selection, a composition of 75(Pt) 25(M) was found to be... 

However, this behavior cannot be depended on. It is safer to monitor hydrogen uptake. Reduction of 4-oxo-slowed down at the ethylene stage although in other compounds, the same catalyst did give spontaneously selective reductions. 

Nevertheless, we should admit the major conclusion of the study by Morrison [8] that the task of attaining selectivity of gas sensors while using catalysts differs from that to obtain selectivity in catalytic reaction as justified. During gas detection one should make use of selectivity of reactants and the stress is placed on the study of capability to accelerate or slow down reaction of above particles whereas catalysis requires a selectivity with respect to products obtained necessitating tiie studies and monitoring of all stages of the process. Therefore, the direct use of catalysts of known reactions does not ensure obtaining desired results. However, in the cases when side products and reaction products do not... 

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