Condensation reactions such as Guerbet and aldol are important since they allow for C-C bond formation and give higher molecular weight oxygenates. An initial study identified Pd-supported on hydrotalcite as an active catalyst for the transformation, although this catalyst showed extensive undesirable decarbonylation. A catalyst containing Pd and Cu in a 3:1 ratio dramatically decreased decarbonylation, while preserving the high catalytic rates seen with Pd-based catalysts. A combination of XRD, EXAFS, TEM, and CO chemisorption and TPD revealed the formation of CuPd bimetallic nanoparticles with a Cu-enriched surface. Finally, density functional theory studies suggest that the surface segregation of Cu atoms in the bimetallic alloy catalyst produces Cu sites with increased reactivity, while the Pd sites responsible for unselective decarbonylation pathways are selectively poisoned by CO.

This study explores the degree to which GGA, meta-GGA, hybrid GGA, and hybrid meta-GGA functionals of density functional theory (DFT), when used with the 6-31+G(d) basis set, are able to reproduce the MP2/6-31+G(d) structures and energetics of the species involved in the reactions of halomethyllithium carbenoids with ethylene. While many popular DFT functionals have been parametrized and/or benchmarked using various databases, the scarcity of experimental structural and energetic information for organolithium compounds has resulted in their exclusion from these training and test sets. In this work, we first establish a set of practical benchmark reaction energetics against which the performance of DFT methods for larger molecules can be compared. Next, we examine the performance of 13 DFT functionals spanning the second, third, and fourth rungs of the "Jacob's ladder" using 84 molecules and 78 reactions. The main conclusions are (a) the meta-hybrid GGA M06-2X is the best functional among the set for organolithium chemistry, (b) the hybrid GGA PBE1PBE consistently yields equilibrium and transition-state geometries that are very close to the MP2 predictions, and (c) MP2//M06-L or MP2//PBE1PBE model chemistries are excellent low-cost alternatives to the costly MP2. However, this work also showed that the very popular B3LYP functional is a rather poor choice for these systems.

Computational catalysts screening is an increasingly popular technique, in which the mechanism from a known good catalyst is commonly adopted, parameterized from linear scaling relationships, and then used in a microkinetic model to identify other metal alloys with incrementally improved activity. This strategy, however, fails to identify truly novel catalysts that operate under nontraditional reaction conditions and exhibit alternative dominant reaction pathways. Using methane oxidation and reforming we investigated a series of O* and OH*‐assisted C‐H scission and C‐O bond formation pathways. Notably, for methane oxidation we discovered a second local optimum for O*‐assisted C‐H bond activation near Ag, which is inactive if only the direct C‐H scission route is considered. In light of the significant qualitative difference in the predicted catalytic trends when parallel mechanisms are allowed, we propose a minimum barrier assumption to rapidly screen for potentially important alternative pathways without the need for costly density functional theory simulations. © 2016 American Institute of Chemical Engineers AIChE J, 63: 66–77, 2017

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