ABSTRACT
The tandem CO2 hydrogenation to hydrocarbons over mixed metal oxide/zeolite catalysts (OXZEO) is an efficient way of producing value-added hydrocarbons (platform chemicals and fuels) directly from CO2via methanol intermediate in a single reactor. In this contribution, two MAPO-18 zeotypes (M = Mg, Si) were tested and their performance was compared under methanol-to-olefins (MTO) conditions (350 °C, PCH3OH = 0.04 bar, 6.5 gCH3OH h-1 g-1), methanol/CO/H2 cofeed conditions (350 °C, PCH3OH/PCO/PH2 = 1:7.3:21.7 bar, 2.5 gCH3OH h-1 g-1), and tandem CO2 hydrogenation-to-olefin conditions (350 °C, PCO2/PH2 = 7.5:22.5 bar, 1.4-12.0 gMAPO-18 h molCO2-1). In the latter case, the zeotypes were mixed with a fixed amount of ZnO:ZrO2 catalyst, well-known for the conversion of CO2/H2 to methanol. Focus was set on the methanol conversion activity, product selectivity, and performance stability with time-on-stream. In situ and ex situ Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), solid-state nuclear magnetic resonance (NMR), sorption experiments, and ab initio molecular dynamics (AIMD) calculations were performed to correlate material performance with material characteristics. The catalytic tests demonstrated the better performance of MgAPO-18 versus SAPO-18 at MTO conditions, the much superior performance of MgAPO-18 under methanol/CO/H2 cofeeds, and yet the increasingly similar performance of the two materials under tandem conditions upon increasing the zeotype-to-oxide ratio in the tandem catalyst bed. In situ FT-IR measurements coupled with AIMD calculations revealed differences in the MTO initiation mechanism between the two materials. SAPO-18 promoted initial CO2 formation, indicative of a formaldehyde-based decarboxylation mechanism, while CO and ketene were the main constituents of the initiation pool in MgAPO-18, suggesting a decarbonylation mechanism. Under tandem CO2 hydrogenation conditions, the presence of high water concentrations and low methanol partial pressure in the reaction medium led to lower, and increasingly similar, methanol turnover frequencies for the zeotypes. Despite both MAPO-18 zeotypes showing signs of activity loss upon storage due to the interaction of the sites with ambient humidity, they presented a remarkable stability after reaching steady state under tandem reaction conditions and after steaming and regeneration cycles at high temperatures. Water adsorption experiments at room temperature confirmed this observation. The faster activity loss observed in the Mg version is assigned to its harder Mg2+-ion character and the higher concentration of CHA defects in the AEI structure, identified by solid-state NMR and XRD. The low stability of a MgAPO-34 zeotype (CHA structure) upon storage corroborated the relationship between CHA defects and instability.
ABSTRACT
This paper studies the performance of the blood flow starting from stenotic human adult femoral arteries with different grades of obstruction, removed from autopsies and surgical amputations, and from simulations produced by an original simulator computerized software based on the method of finite elements for newtonian, homogeneous and uncompressible fluids. Its employment generated numerous maximal curves, subsequently joined in a unique graphic of easy application. Exceeding the evaluation of the origin and impact of turbulences by analyzing the different variables involved in such anomalous conditions (i.e: pressure, velocity field and stress tensor), the results here reported may constitute a useful complementary diagnostic method together the others used at present.
Subject(s)
Computer Simulation , Femoral Artery/physiopathology , Vascular Diseases/physiopathology , Blood Pressure , Constriction, Pathologic/diagnosis , Constriction, Pathologic/physiopathology , Humans , Male , Middle Aged , Regional Blood Flow , Vascular Diseases/diagnosisABSTRACT
El presente trabajo estudia el comportamiento del flujo sanguíneo a partir de arterias femorales humanas estenóticas con distintos grados de obstrucción, extraídas de autopsias y de amputaciones quirúrgicas y de simulaciones producidas por un programa computacional simulador original basado en el método de los elementos finitos para líquidos newtonianos, homogéneos e incompresibles. Su empleo produjo numerosas curvas de máxima resumidas en un único gráfico de aplicación sencilla para el profesional. Más allá de la evaluación del origen y del impacto de los remolinos analizando las distintas variables intervinientes (esto es: presión, velocidad y tensiones), los resultados aquí reportados pueden constituir un útil complemento diagnóstico junto a los demás métodos usados actualmente, a los que no contraviene ni invalida. (AU)
Subject(s)
Humans , Male , Middle Aged , Femoral Artery/pathology , Computer Simulation , Femoral Artery/physiopathology , Constriction, Pathologic/diagnosis , Constriction, Pathologic/pathology , Constriction, Pathologic/physiopathology , Regional Blood Flow , Blood PressureABSTRACT
El presente trabajo estudia el comportamiento del flujo sanguíneo a partir de arterias femorales humanas estenóticas con distintos grados de obstrucción, extraídas de autopsias y de amputaciones quirúrgicas y de simulaciones producidas por un programa computacional simulador original basado en el método de los elementos finitos para líquidos newtonianos, homogéneos e incompresibles. Su empleo produjo numerosas curvas de máxima resumidas en un único gráfico de aplicación sencilla para el profesional. Más allá de la evaluación del origen y del impacto de los remolinos analizando las distintas variables intervinientes (esto es: presión, velocidad y tensiones), los resultados aquí reportados pueden constituir un útil complemento diagnóstico junto a los demás métodos usados actualmente, a los que no contraviene ni invalida.
Subject(s)
Humans , Male , Middle Aged , Computer Simulation , Femoral Artery/pathology , Blood Pressure , Constriction, Pathologic/diagnosis , Constriction, Pathologic/pathology , Constriction, Pathologic/physiopathology , Femoral Artery/physiopathology , Regional Blood FlowABSTRACT
This paper studies the performance of the blood flow starting from stenotic human adult femoral arteries with different grades of obstruction, removed from autopsies and surgical amputations, and from simulations produced by an original simulator computerized software based on the method of finite elements for newtonian, homogeneous and uncompressible fluids. Its employment generated numerous maximal curves, subsequently joined in a unique graphic of easy application. Exceeding the evaluation of the origin and impact of turbulences by analyzing the different variables involved in such anomalous conditions (i.e: pressure, velocity field and stress tensor), the results here reported may constitute a useful complementary diagnostic method together the others used at present.
