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Microwave-assisted gas-phase conversion on structured catalysts is emerging as a promising process intensification technology in the field of heterogeneous catalysis. The combination of selective heating and structured catalytic materials induces a temperature difference between the heated catalytic sample and the surrounding void regions to avoid non-selective gas-phase reactions. This operational principle allowed inhibiting thermal cracking in alkane dehydrogenation processes as well as retarding catalyst deactivation by coking in methane dehydroaromatization (MDA) processes. However, its effectiveness has not been reported so far out of the laboratory scale conditions. This work addresses the scaling of the microwave-assisted MDA process from lab scale experiments to a scaled-up configuration capable of stable operation with a 150-fold higher feeding rate. The scaling-up potential and main obstacles to overcome for this technology are critically discussed. In addition, a techno-economic assessment of the MW-MDA process is presented. The catalytic activity was kept for seven consecutive reaction cycles, i.e. 35 h MW-MDA, prior to a progressive decay due to permanent deactivation caused by zeolite dealumination and active metal loss. The scaled set-up operated for up to 295 consecutive hours under unmanned operation conducting 4 -h MDA-regeneration cycles on Mo/ZSM-5@SiC monoliths and resulting in 125-fold increase of converted methane and a 450-fold increase of benzene (0.17 LC6H6/h) in comparison with the laboratory scale tests. Scaled set-up experiments were run using only a 6-fold microwave input power, thus, highlighting the non-linearity between energy consumption and scaling factor for this technology and the importance of microwave cavity design.

Microwave-assisted heterogeneous catalysis (MHC) is gaining attention due to its exciting prospects related to selective catalyst heating, enhanced energy-efficiency, and partial inhibition of detrimental side gas-phase reactions. The induced temperature difference between the catalyst and the comparatively colder surrounding reactive atmosphere is pointed as the main factor of the process selectivity enhancement towards the products of interest in a number of hydrocarbon conversion processes. However, MHC is traditionally restricted to catalytic reactions in the absence of catalyst coking. As excellent MW-susceptors, carbon deposits represent an enormous drawback of the MHC technology, being main responsible of long-term process malfunctions. This work addresses the potentials and limitations of MHC for such processes affected by coking (MHCC). It also intends to evaluate the use of different catalyst and reactor configurations to overcome heating stability problems derived from the undesired coke deposits. The concept of long-term MHCC operation has been experimentally tested/applied to for the methane non-oxidative coupling reaction at 700 °C on Mo/ZSM-5@SiC structured catalysts. Preliminary process scalability tests suggest that a 6-fold power input increases the processing of methane flow by 150 times under the same controlled temperature and spatial velocity conditions. This finding paves the way for the implementation of high-capacity MHCC processes at up-scaled facilities.

Platinum–rare-earthalloys have proven to be both active and stable under accelerated stability tests in their bulk polycrystalline form. However, a scalable method for the synthesis of a high-surface-area supported catalyst of these alloys has so far not been presented. Herein we discuss the thermodynamics relevant for the reduction conditions of the rare earths to form alloys with platinum. We show how the tolerance for water and oxygen severely limits the synthesis parameters and how under certain conditions the thermal reduction of YCl3 with H2 is possible from 500 °C. From the insight gained, we synthesized a PtxY/C catalyst by modifying a Pt/C catalyst and confirmed alloy formation by both X-ray diffraction and X-ray photoelectron spectroscopy measurements.These reveal crystalline intermetallic phases and the metallic state of yttrium. Without any optimization of the method, the catalyst has an improved mass activity in comparison to the unmodified catalyst,proving the viability of the method. Initial work based on thermodynamic equilibrium calculations on reduction time show promise in controlling the phase formed by tuning the parameters of time, temperature, and gas composition.

PtxY and PtxGd exhibit exceptionally high activity for oxygen reduction, both in the polycrystalline form and the nanoparticulate form. In order to understand the origin of the enhanced activity of these alloys, we have investigated thin films of these alloys on bulk Pt(111) crystals, i.e. Y/Pt(111) and Gd/Pt(111). These surfaces exhibit a 4-fold improvement over Pt(111). We observe the formation of a thick Pt overlayer after the electrochemical measurements, both on Y/Pt(111) and Gd/Pt(111). Using surface sensitive X-ray diffraction we revealed that crystalline closely packed Pt overlayers were formed. The diffraction experiments showed that the strain and crystallinity of the overlayers are strongly dependent on the electrochemical treatment, and in general show lateral compression.