Theoretical investigation of n-butane isomerization in metal-substituted aluminosilicates

Der stetige Anstieg an Treibhausgasen in unserer Atmosphäre, welche der Grund für den konstanten Anstieg der Temperatur der Erde sind, beruht zu einem großen Teil auf der Emission dieser Gase, z.B. von Kohlenstoffdioxid (CO$_2$), durch industrielle Prozesse. Speziell in der petrochemischen Industrie wird eine große Menge an CO$_2$ durch Flaring von ungewollten leichten Kohlenwasserstoffen, wie z.B. Butan, produziert. Um das Problem des Klimawandels, welches auf dem erhöhten Ausstoß von Treibhausgasen beruht, zu bekämpfen, is es von hoher Wichtigkeit, diese Nebenprodukte effizient zu nutzen. Im Fall von Butan ist eine katalytische Isomerisierung zu Isobutan möglich. Isobutan ist ein sehr viel wertvolleres Molekül aufgrund der diversen Verwendungsmöglichkeiten in der Industrie, z.B. zur Verbesserung der Oktanzahl von Benzin oder in der Synthese von Methyl-tert-butyl-ether (MTBE) via Isobutylen. Jedoch enthalten gegenwärtig für diese Reaktion verwendete Katalysatoren toxische Komponenten, wodurch deren Verwendung gefährlich und umweltschädlich ist. Daher ist eine gründliche und breite Forschung notwendig, um effizientere, billigere und umweltfreundlichere Katalysatoren für die Isomerisierung von n-Butan zu Isobutan zu entdecken. In dieser Arbeit wird dieses Problem rechnerisch mithilfe von sehr genauen Dichtefunktionaltheorie (DFT) Rechnungen angegangen. Die zugrundeliegenden Mechanismen der n-Butan Isomerisierung werden mithilfe eines Modell-Katalysators, H-SSZ-13 (CHA), untersucht, welcher kostengünstig und einfach zu berechnen ist. Die zwei in der Literatur ausgiebig diskutierten Reaktionspfade für die Isomerisierung von 2-Buten, nämlich der monomolekulare und der bimolekulare Mechanismus, werden in dem Zeoliten H-SSZ-13 optimiert und miteinander verglichen. Zusätzlich wurden zwei weitere Reaktionsmechanismen vorgestellt, der (intermolekulare) Wasserstoff-Transfer-Mechanismus und der Methyl-Transfer-Mechanismus. Ersterer zeigt eine Möglichkeit auf, wie Olefine, welche während der Reaktion gebildet werden, die Reaktion selbst katalysieren können, während letzterer einen zweiten Reaktionspfad beschreibt, durch welchen die Bildung von ungewünschten Nebenprodukten der Reaktion erklärt werden können. Die Reaktionsbarrieren wurden für alle Mechanismen mithilfe sehr genauer Methoden berechnet. Diese Barrieren zeigen, dass für den Zeolit H-SSZ-13 mit einer Barriere von 152 kJ/mol bei einer Temperatur von 400 °C der monomolekulare Mechanismus gegenüber dem bimolekularen Mechanismus bevorzugt wird. Der Wasserstoff-Transfer-Mechanismus hat eine eher hohe freie Barriere der freien Energie von 203 kJ/mol, während die Barriere für den Methyl-Transfer-Mechanismus mit 227 kJ/mol sehr hoch und daher bei den betracheten Reaktionsbedingungen nicht plausibel ist. Diese Reaktionsmechanismen werden anschließend in einer Reihe von verschiedenen Zeoliten und Zeotypen von CHA, AFI und MOR neu optimiert. Für den monomolekularen Mechanismus werden abhängig von dem konkreten Zeoliten unterschiedliche Reaktionspfade als optimal berechnet. Für Zeolite, welche eine höhere Azidität aufweisen, wie es für AFI der Fall ist, wird der bimolekulare Mechanismus als konkurrierend oder sogar als dominant gegenüber den monomolekularen Mechanismus berechnet. Die Barrieren des Wasserstoff-Transfer-Mechanismus reichen von 181 kJ/mol bis 236 kJ/mol, was bedeutet, dass diese im Fall von stark aziden Zeoliten berücksichtigt werden müssen, während der Methyl-Transfer-Mechanismus nur Barrieren von $\geq$217 kJ/mol aufzeigt. Alle Resultate werden schlussendlich mittels linearer Skalierungsbeziehungen zusammengefasst, welche sich auf die Adsorptionsenergie von Ammoniak als Deskriptor beziehen. Es ist bekannt, dass diese Skalierungsbeziehungen Tendenzen in der Reaktivität von Zeolit-Katalysatoren voraussagen können, und dies gilt auch hier für die in dieser Arbeit untersuchten Reaktionsmechanismen

Palaeotsunamis in the Sino-Pacific region

© 2020 Elsevier B.V. Palaeotsunami research in the Sino-Pacific region has increased markedly following the 2011 Tōhoku-oki tsunami. Recent studies encompass a variety of potential sources and cover a full range of research activities from detailed studies at individual sites through to region-wide data collation for the purposes of database development. We synthesise palaeotsunami data from around the region drawing on key examples to highlight the progress made since 2011. We focus on a wide range of spatial and temporal scales, from region-wide to local events, from multi-millennial site records to estimates of magnitude and frequency along national coastlines. The review is based on sub-regions but in reviewing the combined records highlights common events and anomalies. In doing so we identify future research opportunities and notable findings arising from our review

Sedimentological analysis of tsunami deposits along the coast of Peru

The Peru-Chile-Trench is one of the most active seismic areas in the world (Kulikov et al., 2005). The subduction of the Nasca Plate under the South American Plate causes earthquakes with magnitudes greater than 8 every 5 to 10 years. Consequently, the risk for destructive tsunami along the coast of Peru is very high. The greatest historical tsunami events in this region are the two Arica tsunami in 1604 and 1868 (Okal et al., 2006) and the Chile tsunami in 1960 (Cisternas et al., 2005). The most recent tsunami are the Chimbote tsunami in 1996 (Bourgeois et al., 1999) and the Camaná tsunami in 2001 (Jaffe et al., 2003). Additionally, in 2007, a magnitude 7.9 earthquake 150 kilometres SSE of Lima generated a tsunami with run up heights of 10 m along the southern Paracas Peninsula (Fritz et al., 2008). Despite a large increase in tsunami studies in the last years, there is still no complete tsunami facies model. Furthermore the hydrodynamical processes leading to deposition of sediment by a tsunami wave are still not well understood. We surveyed various locations along the 2400 km Peruvian coastline to locate deposits of recent and historical tsunami events. Deposits were studied in trenches and boreholes down to depths of 3 m. We separated the foraminifera content for identification and inference of water depths of sediment entrainment by the tsunami. The grain-size distributions of the sampled deposits were optically determined with a PartAn 2001 particle analyser. The grain-size data were used to re-model the flow depths, using the inverse tsunami model of Jaffe & Gelfenbaum (2007)

Seismites and paleotsunamis deposits, assessing for paleoseismicity in Peru

[ENG] Human occupation records in Perú provide historical record of large earthquakes prior to the 20th century. In this study, we extend our knowledge of major events by evaluating the stratigraphy and chronology of sediments exposed in various sectors of the Central Andes. These observations suggests that strong seismic activity occurred during the Quaternary, either along the subduction megathrust or on crustal faults. Indeed in Cusco and Colca regions, ,active faults affect fluvio-glacial and alluvial Holocene to Pliocene deposits. High in the topography, lacustrine deposits as well as Quaternary moraines display multiple geomorphic evidences of displacements ans seismites attesting for regional seismotectonic activity. Similarly along the Peruvian coast, 90 excavations succeeded in identifying for the first time paleo-tsunami deposits in southern Peru. Among them, the most impressive are encountered in Puerto Casma and Boca Rio and sign the historic 1619 subduction event and former unknown events (1641 ± 26 years B.P. ie 1668, as well as 2.26 ± 0.37 ka and 1.98 ± 0.23 ka respectively)

Sedimentological aspects of recent and historical tsunami events along the coast of Peru

The coast of Peru is greatly endangered by tsunami events. The subduction of the Nasca Plate below the South American Plate triggers strong submarine earthquakes that are capable of causing tsunami. High-energy wave events are major coast shaping processes. In some regions, e.g. the Caribbean, a distinction between storm/hurricane and tsunami deposits is difficult. Therefore, the absence of heavy storms makes the Peruvian coast a good target for tsunami research. Other meteorological phenomena, like El Niño events that occur in Peru are not associated with strong storms or surges. Deposits of El Niño-caused flooding can easily be distinguished from tsunami events, since their sedimentary structures imply transport from the land to the sea, the deposited material derives from the mountain ranges and no indicators (e.g., foraminifera, shells) of marine inundations are present. In our study we re-surveyed locations of the three most recent regional tsunami events in order to learn about the sedimentary structures and their preservation potential. We visited the areas affected by the Chimbote-Tsunami of 21st February 1996 (5 m run up; Bourgeois et al., 1999; Kulikov et al., 2005), by the Camana-Tsunami of the 23rd June 2001 (9 m run up; Jaffe et al., 2003) and by the Pisco-Paracas-Tsunami of 15th August 2007 (10 m run up; Fritz et al., 2007). Secondly, we surveyed the coast of Peru in order to find traces of historical or paleotsunami events. All sediments were sampled for grain size analysis, foraminifera determination and optically stimulated luminescence dating. For historical events, the inverse tsunami model of Jaffe & Gelfenbaum (2007) was applied to calculate onshore tsunami flow depths. Both recent and historical tsunami deposits are present as (1) (graded) layers of coarse sand, some including shell fragments or pieces of rock, (2) (imbricated) shell layers, (3) heavy mineral accumulations and (4) mud caps or mud balls. Imbricated shells can give information on flow directions and hence can help to distinguish between run up and backwash sediments. Unfortunately, the preservation potential of onshore tsunami deposits is very low. Erosion by wind, rivers or heavy rain falls (e.g., during El Niño events) and bioturbation (e.g., by crabs) can modify or destroy the sediments. For recent events, human activity (e.g., the use of beach / tsunami sand for rebuilding) is a limiting preservation factor. This study shows that muddy tsunami sediments and backwash sediments have the highest preservation potential. This is due to the cohesion of mud that makes the deposits less sensitive for erosion during backwash and due to fast hardening of mud layers in the dry Peruvian climate

Sedimentological analysis of the Ordovician and Devonian basins in southern Peru and northern Bolivia

We present data from a study of the evolution of the Early Paleozoic Peru-Bolivia Trough, its facies development and the provenance of sediments deposited during Ordovician and Devonian time. We measured and sampled sections in the Ordovician successions in the Cordillera Oriental of southern Peru (Ollantaytambo, Verónica, San José, Sandia and Calapuja Formations) and northern Bolivia (Coroico, Amutara and Cancañiri Formations), and in the Upper Silurian to Devonian Lampa Formation on the Altiplano, and the Devonian Cabanillas Group on the Altiplano and the Peruvian Coastal Cordillera (Arequipa Massif). Our data contribute to a better understanding of the plate tectonic evolution of the Western Gondwana margin during early Paleozoic times

Sedimentología y dataciones por luminiscencia estimulada ópticamente (OSL) de depósitos de paleotsunamis a lo largo de la costa peruana

La costa del Pacífico fue testigo de innumerables tsunamis desde la formación de la margen y seguirán ocurriendo por millones de años más, es así que se reportan olas de hasta 20 m (Kulikov et al., 2005), generando extensa destrucción y pérdidas de vidas. Lockrige (1985), determina según estadísticas que entre Perú y Chile son los países que sufren más terremotos y erupciones volcánicas por kilómetro cuadrado en todo el planeta. Sólo si se considera el siglo XX, uno de cada tres tsunamis del Océano Pacífico se originó en las costas peruanas y/o chilenas. A fines de los ochenta, la aparición de dos publicaciones generó un importante cambio en la forma de evaluar el riesgo de tsunami. Atwater (1987) observó capas de sedimentos arenosos anómalas en la estratigrafía palustre, interpretándolos como depósitos prehistóricos de tsunamis. Posteriormente, Dawson et al. (1988) describió un inusual depósito contenido en la estratigrafía de la costa de Escocia, explicándolo como el resultado de un mega-tsunami producido por la avalancha submarina Storegga ocurrida hace 8 100 años en el norte de Europa. Tanto Atwater (1987) como Dawson et al. (1988) enfrentaron dificultades en sus interpretaciones, debido a que no fue posible, en aquel tiempo demostrar que aquellos estratos fueran similares a los depósitos dejados por tsunamis modernos, pues nunca habían sido estudiados. Así, Atwater (1987) utilizó información sismológica de un gran terremoto (1700 DC), para sustentar que un tsunami, inducido por aquel sismo, había depositado dichos sedimentos. A pesar de la importancia de los sismos y tsunamis en Perú, existen muy pocos estudios científicos relacionados a los registros sedimentarios y geomorfológicos dejados por estos eventos en el litoral de nuestro país. En el presente trabajo presentamos resultados sobre la sedimentología y dataciones de los depósitos de tsunami a lo largo de la margen peruana utilizando OSL como técnica de datación

Combining Theoretical and Experimental Methods to Probe Confinement within Microporous Solid Acid Catalysts for Alcohol Dehydration

Catalytic transformations play a vital role in the implementation of chemical technologies, particularly as society shifts from fossil-fuel-based feedstocks to more renewable bio-based systems. The dehydration of short-chain alcohols using solid acid catalysts is of great interest for the fuel, polymer, and pharmaceutical industries. Microporous frameworks, such as aluminophosphates, are well-suited to such processes, as their framework channels and pores are a similar size to the small alcohols considered, with many different topologies to consider. However, the framework and acid site strength are typically linked, making it challenging to study just one of these factors. In this work, we compare two different silicon-doped aluminophosphates, SAPO-34 and SAPO-5, for alcohol dehydration with the aim of decoupling the influence of acid site strength and the influence of confinement, both of which are key factors in nanoporous catalysis. By varying the alcohol size from ethanol, 1-propanol, and 2-propanol, the acid sites are constant, while the confinement is altered. The experimental catalytic dehydration results reveal that the small-pore SAPO-34 behaves differently to the larger-pore SAPO-5. The former primarily forms alkenes, while the latter favors ether formation. Combining our catalytic findings with density functional theory investigations suggests that the formation of surface alkoxy species plays a pivotal role in the reaction pathway, but the exact energy barriers are strongly influenced by pore structure. To provide a holistic view of the reaction, our work is complemented with molecular dynamics simulations to explore how the diffusion of different species plays a key role in product selectivity, specifically focusing on the role of ether mobility in influencing the reaction mechanism. We conclude that confinement plays a significant role in molecular diffusion and the reaction mechanism translating to notable catalytic differences between the molecules, providing valuable information for future catalyst design