Structure–performance descriptors and the role of Lewis acidity in the methanol-to-propylene process

The combination of well-defined acid sites, shape-selective properties and outstanding stability places zeolites among the most practically relevant heterogeneous catalysts. The development of structure-performance descriptors for processes that they catalyse has been a matter of intense debate, both in industry and academia, and the direct conversion of methanol to olefins is a prototypical system in which various catalytic functions contribute to the overall performance. Propylene selectivity and resistance to coking are the two most important parameters in developing new methanol-to-olefin catalysts. Here, we present a systematic investigation on the effect of acidity on the performance of the zeolite 'ZSM-5' for the production of propylene. Our results demonstrate that the isolation of Bronsted acid sites is key to the selective formation of propylene. Also, the introduction of Lewis acid sites prevents the formation of coke, hence drastically increasing catalyst lifetime

HAMSTAD benchmarks using Comsol revisited

Benchmarks are important tools to verify computational models. In the research area of building physics, the so-called HAMSTAD (Heat, Air and Moisture STAnDardization) project is a very well known benchmark for the testing of simulation tools. In this paper we revisit this benchmark by modeling all five subtasks using Comsol 5.2. Again we conclude that Comsol provides satisfactory results on all benchmarks

Simulating the complete HAMSTAD benchmark using a single model implemented in Comsol

Benchmarks are important tools to verify computational models. In the research area of building physics, the so-called HAMSTAD (Heat, Air and Moisture STAnDardization) project is a very well known benchmark for the testing of simulation tools. In contrast to earlier work where we used multiple (Comsol) models, in this paper we simulated all five subtasks of the benchmark by using a single model implemented in Multiphysics software Comsol 5.2a. We conclude that the single model provides satisfactory results on all parts of the benchmark and is therefore applicable for a wide range of HAM problems

Dynamics and sequential analysis of a mesotidal shoal and intershoal channel complex in the Eastern Scheldt (southwestern Netherlands)

A detailed survey was carried out on a mesotidal shoal and intershoal channel complex near the mouth of the Eastern Scheldt in the southwestern part of The Netherlands during the summers of 1976 and 1977. The objectives were to establish a relationship between the morphological changes through time and its influence on the development of the preserved sedimentary sequence. The investigated area is divided into four zones, each one characterized by specific depositional processes and their related bedforms: (a) the outer channel bend and margin, which is mainly covered by flood-oriented large-scale catenary ripples and sand waves; (b) the channel thalweg and inner bend, which is dominated by ebb-oriented mega-ripples; (c) the inner channel margin, which is characterized by a levee wall; (d) the adjacent shoal areas, which generally are flat but may be covered by patches of flood- or ebb-oriented large-scale ripples. The preserved vertical sequence of sedimentary structures in each zone is more or less in accordance with the presence of the dominant bedforms within the respective zones. Sequential analysis shows that the net sedimentation within the outer channel margin is much less when compared to the sediment accumulation within the inner channel margin. This means that the lateral accretional units of the inner channel margin are a dominant feature within the preserved sequence of such a shoal and intershoal channel complex, and also that the preservation potential of sedimentary structures in the inner margin sequence is considerable higher as that compared to the outer margin sequence. Consequently, preservation of the megaripples, a major bedform in a large part of the investigated area, will be limited and will form only a minor part within an ancient analoguous sequence