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In a hybrid catalyst process, syngas is converted, via a methanol intermediate, into a mixture of short-chain hydrocarbons over a combined methanol synthesis catalyst and molecular sieve. It operates under process conditions where the hydrogen partial pressure is relatively high vs the (intermediate) methanol partial pressure. We show that, under these conditions, the lifetime of the molecular sieve (SAPO-34) is greatly enhanced and the amount and type of carbon on the spent catalyst are vastly different as compared to those in a methanol to olefins (MTO) process. The impact of the hydrogen partial pressure, temperature, and methanol partial pressure is studied, leading to a conceptual model of coke deposition and removal. This allows the identification of process conditions that lead to a stable and long lifetime of SAPO-34 in a direct syngas-to-hydrocarbons process.

The influence of carbon on the adsorption of CO from a Rh(100) single crystal has been studied by a combination of experimental techniques: Temperature Programmed Desorption (TPD), Low Energy Electron Diffraction (LEED), and High Resolution Electron Energy Loss Spectroscopy (HREELS). These experimental techniques were combined with a computational approach using Density Functional Theory (DFT). Using this combination of techniques, we have shown that surface carbon greatly influences adsorbed CO and we have determined the exact magnitude of this interaction. Furthermore, we have demonstrated that carbon does not remain fully on the surface; at higher coverage it diffuses partially to subsurface positions. The presence of these subsurface species significantly influences the adsorbates on the surface.

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