Since its commercial introduction three-quarters of a century ago, fluid catalytic cracking has been one of the most important conversion processes in the petroleum industry. In this process, porous composites composed of zeolite and clay crack the heavy fractions in crude oil into transportation fuel and petrochemical feedstocks. Yet, over time the catalytic activity of these composite particles decreases. Here, we report on ptychographic tomography, diffraction, and fluorescence tomography, as well as electron microscopy measurements, which elucidate the structural changes that lead to catalyst deactivation. In combination, these measurements reveal zeolite amorphization and distinct structural changes on the particle exterior as the driving forces behind catalyst deactivation. Amorphization of zeolites, in particular, close to the particle exterior, results in a reduction of catalytic capacity. A concretion of the outermost particle layer into a dense amorphous silica–alumina shell further reduces the mass transport to the active sites within the composite.

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Anisotropic uniform single-crystal nanostructures of α-MoO3 have been synthesized successfully via a novel green and facile approach, i.e., decomposition and condensation of peroxomolybdic acid under hydrothermal conditions. The structure and morphology of the products were characterized by means of X-ray diffraction, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, thermogravimetric/differential thermal analysis, temperature programmed decomposition-mass spectrometry, and Fourier transform infrared spectroscopy. It has been found that the formation of α-MoO3 proceeds at hydrothermal temperatures higher than 83.5 °C and that of MoO2.67(O2)0.33·0.75H2O is at 81.5 °C with the 0.9 mol/L molybdenum solution. The as-synthesized uniform nanostructures grow preferentially along [001], and the dimensions are 200−330 nm in width, 60−90 nm in thickness, and up to 10 μm in length during time spans from 20 to 45 h at 170 °C. The structure and morphology of α-MoO3 show a weak dependence on the molybdenum concentrations of 0.2−0.9 mol/L, while the growth in the b-axis direction can be enhanced distinctly and specifically by the addition of nitric acid to the initial peroxomolybdic acid solution. The critical point in temperature (81.5−83.5 °C) to form hydrate and oxide is discussed, and one possible mechanism is proposed.

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Porosity in catalyst particles is essential because it enables reactants to reach the active sites and it enables products to leave the catalyst. The engineering of composite-particle catalysts through the tuning of pore-size distribution and connectivity is hampered by the inability to visualize structure and porosity at critical-length scales. Herein, it is shown that the combination of phase-contrast X-ray microtomography and high-resolution ptychographic X-ray tomography allows the visualization and characterization of the interparticle pores at micro- and nanometer-length scales. Furthermore, individual components in preshaped catalyst bodies used in fluid catalytic cracking, one of the most used catalysts, could be visualized and identified. The distribution of pore sizes, as well as enclosed pores, which cannot be probed by traditional methods, such as nitrogen physisorption and isotherm analysis, were determined.

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