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1. Improving alkane dehydrogenation activity on γ-Al 2 O 3 through Ga doping

   https://doi.org/10.1039/d0cy01474e  

   Abdelgaid, Mona ; Dean, James ; Mpourmpakis, Giannis ( November 2020 , Catalysis Science & Technology)

   null (Ed.)

   Nonoxidative alkane dehydrogenation is a promising route to produce olefins, commonly used as building blocks in the chemical industry. Metal oxides, including γ-Al 2 O 3 and β-Ga 2 O 3 , are attractive dehydrogenation catalysts due to their surface Lewis acid–base properties. In this work, we use density functional theory (DFT) to investigate nonoxidative dehydrogenation of ethane, propane, and isobutane on the Ga-doped and undoped (100) γ-Al 2 O 3 via the concerted and stepwise mechanisms. We revealed that doping (100) γ-Al 2 O 3 with Ga atoms has significant improvement in the dehydrogenation activity by decreasing the C–H activation barriers of the kinetically favored concerted mechanism and increasing the overall dehydrogenation turnover frequencies. We identified the dissociated H 2 binding energy as an activity descriptor for alkane dehydrogenation, accounting for the strength of the Lewis acidity and basicity of the active sites. We demonstrate linear correlations between the dissociated H 2 binding energy and the activation barriers of the rate determining steps for both the concerted and stepwise mechanisms. We further found the carbenium ion stability to be a quantitative reactant-type descriptor, correlating with the C–H activation barriers of the different alkanes. Importantly, we developed an alkane dehydrogenation model that captures the effect of catalyst acid–base surface properties (through dissociated H 2 binding energy) and reactant substitution (through carbenium ion stability). Additionally, we show that the dissociated H 2 binding energy can be used to predict the overall dehydrogenation turnover frequencies. Taken together, our developed methodology facilitates the screening and discovery of alkane dehydrogenation catalysts and demonstrates doping as an effective route to enhance catalytic activity. 

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2. Selective Conversion of Glycerol to Value‐Added C 3 Products: Effect of Catalyst Surface Structure

   https://doi.org/10.1002/cctc.202201188  

   Gupta, Geet ; Roling, Luke T. ( December 2022 , ChemCatChem)

   Glycerol, a major byproduct of biodiesel processing, could be leveraged as a platform to higher‐value products if the selectivity of its transformations could be improved. Herein, density functional theory (DFT) calculations are used to identify reactivity trends for the initial glycerol dehydrogenation steps involving C−H and O−H bond cleavage on a variety of transition metals including Ag, Au, Cu, Pd, Pt, and Rh considering both (111) and (100) surface facets. Additional activation energies calculated on Pt(111), Pt(100), Au(111), and Au(100) surfaces indicate that the most energetically favorable pathway is highly sensitive to the local surface structure and depends on the adsorption strength of reactive intermediates to the metal surface. Finally, adsorbate‐based and structure‐based energy scaling approaches for glycerol are identified, suggesting the ability to screen candidate materials using both structure‐ and composition‐based reactivity descriptors.

    

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3. First-principles design of a single-atom–alloy propane dehydrogenation catalyst

   https://doi.org/10.1126/science.abg8389  

   Hannagan, Ryan T. ; Giannakakis, Georgios ; Réocreux, Romain ; Schumann, Julia ; Finzel, Jordan ; Wang, Yicheng ; Michaelides, Angelos ; Deshlahra, Prashant ; Christopher, Phillip ; Flytzani-Stephanopoulos, Maria ; et al ( June 2021 , Science)

   The complexity of heterogeneous catalysts means that a priori design of new catalytic materials is difficult, but the well-defined nature of single-atom–alloy catalysts has made it feasible to perform unambiguous theoretical modeling and precise surface science experiments. Herein we report the theory-led discovery of a rhodium-copper (RhCu) single-atom–alloy catalyst for propane dehydrogenation to propene. Although Rh is not generally considered for alkane dehydrogenation, first-principles calculations revealed that Rh atoms disperse in Cu and exhibit low carbon-hydrogen bond activation barriers. Surface science experiments confirmed these predictions, and together these results informed the design of a highly active, selective, and coke-resistant RhCu nanoparticle catalyst that enables low-temperature nonoxidative propane dehydrogenation.

    

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4. Identification of the structure of the Bi promoted Pt non-oxidative coupling of methane catalyst: a nanoscale Pt 3 Bi intermetallic alloy

   https://doi.org/10.1039/C8CY02171F  

   Zhu Chen, Johnny ; Wu, Zhenwei ; Zhang, Xiaoben ; Choi, Slgi ; Xiao, Yang ; Varma, Arvind ; Liu, Wei ; Zhang, Guanghui ; Miller, Jeffrey T. ( March 2019 , Catalysis Science & Technology)

   Recently, stable non-oxidative conversion of methane (NOCM) for up to 8 h with a C 2 selectivity greater than 90% has been reported over Pt–Bi/ZSM-5 at moderate temperatures (600–700 °C). In this study, we show that the structure of the bimetallic nanoparticles on Pt–Bi/ZSM-5 catalyst is similar to Pt–Bi/SiO 2 . EXAFS indicates the formation of Pt-rich bimetallic Pt–Bi nanoparticles with Pt–Bi bond distance of 2.80 Å. The XRD spectra (on SiO 2 ) are consistent with cubic, intermetallic surface Pt 3 Bi phase on a Pt core. The Pt 3 Bi structure is not known in the thermodynamic phase diagram. In all catalysts, only a small fraction of Bi alloys with Pt. At high Bi loadings, excess Bi reduces at high temperature, covering the catalytic surface leading to a loss in activity. At lower Bi loadings with little excess Bi, the Pt 3 Bi surface is effective for non-oxidative coupling of CH 4 (on ZSM-5) and propane dehydrogenation (on SiO 2 ). 

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5. Structural trends in the dehydrogenation selectivity of palladium alloys

   https://doi.org/10.1039/d0sc00875c  

   Purdy, Stephen C. ; Seemakurthi, Ranga Rohit ; Mitchell, Garrett M. ; Davidson, Mark ; Lauderback, Brooke A. ; Deshpande, Siddharth ; Wu, Zhenwei ; Wegener, Evan C. ; Greeley, Jeffrey ; Miller, Jeffrey T. ( May 2020 , Chemical Science)

   null (Ed.)

   Alloying is well-known to improve the dehydrogenation selectivity of pure metals, but there remains considerable debate about the structural and electronic features of alloy surfaces that give rise to this behavior. To provide molecular-level insights into these effects, a series of Pd intermetallic alloy catalysts with Zn, Ga, In, Fe and Mn promoter elements was synthesized, and the structures were determined using in situ X-ray absorption spectroscopy (XAS) and synchrotron X-ray diffraction (XRD). The alloys all showed propane dehydrogenation turnover rates 5–8 times higher than monometallic Pd and selectivity to propylene of over 90%. Moreover, among the synthesized alloys, Pd 3 M alloy structures were less olefin selective than PdM alloys which were, in turn, almost 100% selective to propylene. This selectivity improvement was interpreted by changes in the DFT-calculated binding energies and activation energies for C–C and C–H bond activation, which are ultimately influenced by perturbation of the most stable adsorption site and changes to the d-band density of states. Furthermore, transition state analysis showed that the C–C bond breaking reactions require 4-fold ensemble sites, which are suggested to be required for non-selective, alkane hydrogenolysis reactions. These sites, which are not present on alloys with PdM structures, could be formed in the Pd 3 M alloy through substitution of one M atom with Pd, and this effect is suggested to be partially responsible for their slightly lower selectivity. 

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