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Micropore topology and crystal size are two independently adjustable properties that govern the internal mass transport limitations of zeolite catalysts. Deciphering the relative impact of each factor on catalyst performance is often nontrivial owing to the inability to synthesize zeolites with predetermined physicochemical properties. In this study, a series of ZSM-11 (MEL) and ZSM-5 (MFI) catalysts of equivalent acidity, but differing pore architecture, are prepared with well-defined crystal sizes to elucidate the effects of diffusion path length versus topology on catalyst lifetime and selectivity. For these studies, we selected the methanol to hydrocarbons (MTH) reaction to assess the impact of design variables on the hydrocarbon pool (HCP) mechanism. Operando UV-vis microspectroscopy is used to investigate the evolution of active HCP species and heavier aromatic coking species during the transient start up period over both catalysts. Our findings reveal that slight variations in framework topology between MEL and MFI zeolites lead to marked differences in their catalytic performance as well as the evolutionary behavior of HCP species within the zeolite pores. We report that the diffusion limitations imposed by the tortuous channels in ZSM-5 catalysts are analogous to increasing the channel length in ZSM-11 catalysts via larger crystal sizes. Notably, we observe similar (albeit slightly offset) trends in MTH selectivity and HCP speciation for both zeolite framework types; however, differences in pore topology and catalyst size exact different effects on the evolution of intracrystalline hydrocarbon species. Collectively, these findings provide evidence that ZSM-11 is an effective medium-sized pore zeolite catalyst for reactions encumbered by rapid coking that often elicits premature deactivation.

The objective of this study was to estimate the size and chemical quality of the total organic C stock and its partition between above-belowground plant parts and soil at sites with different plant cover induced by sheep grazing in the arid Patagonian Monte. This study was conducted at six representative sites with increasing signs of canopy disturbance attributed to grazing pressure. We used faeces density as a proxy of grazing pressure at each site. We assessed the total plant cover, shrub and perennial grass cover, total standing aboveground biomass (AGB), litter mass and belowground biomass (BGB) at each site. We further estimated the content of organic C, lignin and soluble phenols in plant compartments and the content of organic C, organic C in humic substances (recalcitrant C) and water soluble C (labile C) in soil at each site. Total plant cover was significantly related to grazing pressure. Standing AGB and litter mass decreased with increasing canopy disturbance while BGB did not vary across sites. Total organic C stock and the organic C stock in standing AGB increased with increasing total plant, shrub, and perennial grass cover. The organic C stock in litter mass increased with increasing total plant and shrub cover, while the organic C stock in BGB did not vary across sites. Lignin content in plant compartments increased with increasing total and shrub cover, while soluble phenols content did not change across sites. The organic C stock and the water soluble C content in soil were positively associated with perennial grass cover. Changes in total plant cover induced by grazing pressure negatively affected the size of the total organic C stock, having minor impact on the size of belowground than aboveground components. The reduction of perennial grass cover was reflected in decreasing chemical quality of the organic C stock in soil. Accordingly, plant managerial strategies should not only be focused on the amount of organic C sequestered but also on the chemical quality of organic C stocks since C chemistry could have an important impact on ecosystem functioning. Fil: Larreguy, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina Fil: Carrera, Analía Lorena. Universidad Nacional de la Patagonia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina Fil: Bertiller, Monica Beatriz. Universidad Nacional de la Patagonia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina