We visualize the elemental zoning in an alumina-supported cobalt molybdenum sulfide (CoMoS) catalyst with scanning transmission X-ray microscopy (STXM). We use the Canadian Light Source beamline 10-IDs (SM) unique combination of soft X-ray and tender X-ray STXM to determine the spatial variation of Co, Al, Mo, and S species. The results clearly show the correlation between cobalt and molybdenum and the anticorrelation between cobalt and alumina, confirming that Co is closely associated with the MoS2 phase. The tender X-ray STXM images show that the fresh catalyst particle contains a 50 nm ring of molybdenum oxide encapsulating the supported MoS2 phase. After the reduction at 200 degrees C with H-2, this oxide rim disappears and a uniform MoS2 distribution is found. Upon oxidation at 400 degrees C, the sulfur disappears from the catalyst sample and molybdenum is oxidized from a MoIV sulfide to a mainly tetrahedral MoVI oxide, while cobalt keeps its divalent nature and changes from a CoII sulfide to a CoII oxide.@en

The effect of a severe steaming treatment on the physicochemical properties and catalytic performance of H-SAPO-34 molecular sieves during the methanol-to-hydrocarbons (MTH) reaction has been investigated with a combination of scanning transmission X-ray microscopy (STXM), catalytic testing, and bulk characterization techniques, including ammonia temperature programmed desorption and 27Al and 29Si magic angle spinning nuclear magnetic resonance. For this purpose, two samples, namely a calcined and a steamed H-SAPO-34 catalyst powder, have been compared. It has been found that calcined H-SAPO-34 displays a high selectivity towards light olefins, yet shows a poor stability as compared to a zeolite H-ZSM-5 catalyst. Moreover, insitu STXM at the carbon K-edge during the MTH reaction allows construction of nanoscale chemical maps of the hydrocarbon species formed within the H-SAPO-34 aggregates as a function of reaction time and steam post-treatment. It was found that there is an initial preferential formation of coke precursor species within the core of the H-SAPO-34 aggregates. For longer times on stream the formation of the coke precursor species is extended to the outer regions, progressively filling the entire H-SAPO-34 catalyst particle. In contrast, the hydrothermally treated H-SAPO-34 showed similar reaction selectivity, but decreased activity and catalyst stability with respect to its calcined counterpart. These variations in MTH performance are related to a faster and more homogeneous formation of coke precursor species filling up the entire steamed H-SAPO-34 catalyst particle. Finally, the chemical imaging capabilities of the STXM method at the Al and Si K-edge are illustrated by visualizing the silicon islands at the nanoscale before and after steaming H-SAPO-34@en

H-ZSM-5 catalyst powders before and after a steaming post-treatment have been investigated during the Methanol-To-Hydrocarbons (MTH) process at 350 degrees C. Bulk and surface characterization techniques have been combined with in situ Scanning Transmission X-ray Microscopy (STXM) at the aluminum and carbon K-edge to study the changes in acidity, porosity, reactivity, and aluminum distribution upon steaming. It was found that steaming post-treatment has a positive impact on the stability of H-ZSM-5 without inducing important changes in the MTH activity and selectivity. The lower MTH stability of non-steamed H-ZSM-5 catalyst powder is related to the formation of poly-aromatic compounds in the outer regions of the catalyst particles, as probed with in situ STXM. In contrast, a limited amount of poly-aromatics was found in the outer rim of steamed H-ZSM-5 catalyst particles. These differences occur as a result of the generation of mesoporosity as well as the reduction in the number and strength of acid sites after steaming, as evidenced by the nanoscale imaging of adsorbed pyridine with STXM@en