diffusion resistance and giving a high mechanical strength. These behaviours help maintain high and uniform voidage throughout the lifetime of the catalyst, reducing the rate of pressure drop increase over time. It is essential that the ceramic phases of the catalyst remain stable under the extreme conditions encountered in steam reforming. Key considerations include minimising sintering and phase changes caused by steam exposure by maximising hydrothermal stability and preventing the formation of inactive Ni phases, e.g. spinel-type structures. The mechanical properties of the catalyst are determined by both the inherent characteristics of the support material and its porosity, factors that must be optimised for overall catalyst performance. These properties are mainly influenced by the formulation chemistry, structural design, and production process steps. Carbon formation can lead to unplanned shutdowns Carbon formation remains one of the most persistent threats to catalyst lifetime and reformer tube integrity. It can lead to catalyst deactivation, increased pressure drop, and the development of hot spots that may cause tube damage or rupture. These issues can force plants to reduce throughput or undergo unplanned shutdowns. Carbon formation on the catalyst surface is influenced by surface acidity. Alpha-alumina, a commonly used support material, contains acidic sites that can exacerbate this issue. One effective strategy to reduce surface acidity is the addition of a Group 2 metal such as calcium (Ca), as implemented in Johnson Matthey’s Katalco 57-series catalysts. These basic promoters undergo ion exchange with acid sites to quench acidity. Furthermore, this modification also alters the mechanical and other chemical properties of the support by influencing the interfacial interaction between the support and the active species. This is particularly important as the reducibility of the catalyst is a key contributing factor to its overall performance, given that the reduction of NiO to its active metallic form is required for catalysis to occur. In high-temperature or heavy-feed reforming
duties with an elevated risk of carbon formation, additional protection can be achieved by incorporating potash into the catalyst formulation. Potash promotes the gasification of carbon, shifting the equilibrium away from carbon deposition on both the catalyst and reformer tubes. It is precisely added to form potassium islands within the support structure, Figure 3 Elemental map showing distribution of Ni on cross-section of a conventional catalyst pellet (left) compared to a pellet with optimised Ni distribution (right) “ Carbon formation remains one of the most persistent threats to catalyst lifetime and reformer tube integrity. It can lead to catalyst deactivation, increased pressure drop, and the development of hot spots that may cause tube damage or rupture ” ensuring a controlled and sustained release of potassium throughout the catalyst’s life. This enables continuous carbon gasification while maintaining the structural integrity of the catalyst. Potassium-promoted catalysts are designed to operate in a specific temperature window, and they are more expensive than non-promoted catalysts. Therefore, the strategy for using promoted catalysts in an SMR is optimised and based on feed composition, heat flux, and risk modelling. Reducing catalyst costs with precision Ni engineering Ni is the active metal in most SMR catalysts due to its favourable cost and activity profile.
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