Our understanding of the tectonic development of the African continent and the interplay between its geological provinces is hindered by unevenly distributed seismic instrumentation. In order to better understand the continent, we used long‐period ambient noise full‐waveform tomography on data collected from 186 broadband seismic stations throughout Africa and surrounding regions to better image the upper mantle structure. We extracted empirical Green's functions from ambient seismic noise using a frequency‐time normalization method and retrieved coherent signal at periods of 7–340 s. We simulated wave propagation through a heterogeneous Earth using a spherical finite‐difference approach to obtain synthetic waveforms, measured the misfit as phase delay between the data and synthetics, calculated numerical sensitivity kernels using the scattering integral approach, and iteratively inverted for structure. The resulting images of isotropic, shear wave speed for the continent reveal segmented, low‐velocity upper mantle beneath the highly magmatic northern and eastern sections of the East African Rift System (EARS). In the southern and western sections, high‐velocity upper mantle dominates, and distinct, low‐velocity anomalies are restricted to regions of current volcanism. At deeper depths, the southern and western EARS transition to low velocities. In addition to the EARS, several low‐velocity anomalies are scattered through the shallow upper mantle beneath Angola and North Africa, and some of these low‐velocity anomalies may be connected to a deeper feature. Distinct upper mantle high‐velocity anomalies are imaged throughout the continent and suggest multiple cratonic roots within the Congo region and possible cratonic roots within the Sahara Metacraton.

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Catalytic dehydrogenation of propane over a Pt-based catalyst to propylene has received considerable interests in recent years because this route is able to provide an economical and efficient way to fill the gap between supply and demand in propylene market. The low dispersion of a Pt particle at the support surface and sintering of Pt nanoparticles under the harsh reaction condition are the main challenges in the practical application of this catalyst. Herein, highly efficient Pt/Sn-Beta catalysts are developed for propane dehydrogenation, which exhibits high activity, selectivity, and stability in this reaction. Full characterizations with XRD, STEM, XPS, CO-IR, H2-TPR, and Py-IR techniques on these catalysts reveal that the Pt clusters are localized at the Sn single-site in the zeolitic framework, which allows the generated Pt clusters to be homogeneously dispersed at the surface zeolite. The high performance of Pt/Sn-Beta catalysts under a high reaction temperature is mainly due to a strong interaction between the Pt cluster and Sn-zeolite. An initial propane conversion of 50%, high propylene selectivity of above 99%, low deactivation rate of 0.006 h–1, high TOF of 114 s–1, and good regenerability have been achieved in the Pt-Sn2.00/Sn-Beta catalyst for propane dehydrogenation at 570 °C.

Heterogeneous catalysis occurs on the surface of a catalyst particle in a gas or liquid environment of reactants. The surface of the catalyst particle acts as an active chemical agent directly participating in a chemical reaction performed at a solid–gas or solid–liquid interface. Thus, authentic surface chemistry and the structure of a catalyst particle during catalysis are key descriptors for understanding catalytic performance of this catalyst. However, identification of the authentic surface of a catalyst particle during catalysis is not a simple task. We are far from knowing the fact. Photoelectron spectroscopy is one of the main techniques for characterizing surface of a catalyst since it’s a surface sensitive technique. When used to track the surface of a catalyst particle at relatively high temperature in gas phase in the torr pressure range, it is called near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) or AP-XPS for simplicity. In the last several years, AP-XPS has been used to observe surface chemistry of catalysts of single crystals and nanoparticles of metal, metal oxide, and carbide. In this review, instrumentation of the near ambient pressure X-ray photoelectron spectrometers and observation of catalyst surfaces in gases phase under reaction conditions and during catalysis with AP-XPS are discussed with the following objectives: (1) to present how the surface of a catalyst particle can be characterized in gas phase, (2) to interpret how surface chemistries observed during catalysis are correlated with measured catalytic performances, (3) to demonstrate how the uncovered correlations between surface structures and catalytic performances help to understand catalytic mechanisms at a molecular level, and (4) to discuss challenges and prospects of using AP-XPS to explore the authentic surface of a catalyst under a condition near to an industrial catalytic condition. This review focuses on the application of AP-XPS to studies of catalysis and how the insights gained from AP-XPS studies can be used to achieve fundamental understanding of the catalytic mechanism at a molecular level.

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