Effective control on chemoselectivity in the catalytic hydrogenation of C=Oo verC =Cb onds is uncommon with Pd-based catalysts because of the favored adsorption of C = C bonds on Pd surface.H ere we report au nique orthorhombic PdSn intermetallic phase with unprecedented chemoselectivity towardC =Oh ydrogenation. We observed the formation and metastability of this PdSn phase in situ. During an atural cooling process,t he PdSn nanoparticles readily revert to the favored Pd 3 Sn 2 phase.I nstead, using at hermal quenching method, we prepared ap ure-phase PdSn nanocatalyst. PdSn shows an > 96 %selectivity toward hydrogenating C = Obonds of various a,b-unsaturated aldehydes,h ighest in reported Pdbased catalysts.Further study suggests that efficient quenching prevents the reversion from PdSn-to Pd 3 Sn 2 -structured surface,t he key to the desired catalytic performance.D ensity functional theory calculations and analysis of reaction kinetics providea nexplanation for the observed high selectivity.

Effective control on chemoselectivity in the catalytic hydrogenation of C=O over C=C bonds is uncommon with Pd‐based catalysts because of the favored adsorption of C=C bonds on Pd surface. Here we report a unique orthorhombic PdSn intermetallic phase with unprecedented chemoselectivity toward C=O hydrogenation. We observed the formation and metastability of this PdSn phase in situ. During a natural cooling process, the PdSn nanoparticles readily revert to the favored Pd3Sn2 phase. Instead, using a thermal quenching method, we prepared a pure‐phase PdSn nanocatalyst. PdSn shows an >96 % selectivity toward hydrogenating C=O bonds of various α,β‐unsaturated aldehydes, highest in reported Pd‐based catalysts. Further study suggests that efficient quenching prevents the reversion from PdSn‐ to Pd3Sn2‐structured surface, the key to the desired catalytic performance. Density functional theory calculations and analysis of reaction kinetics provide an explanation for the observed high selectivity.

Reactive flash sintering has been demonstrated as a method to rapidly densify and synthesize ceramic materials, but determining the extent of chemical reactions can be complex since the maximum temperature reached by the sample may be brief in time. The black body radiation (BBR) model has been shown to accurately predict the sample temperature during the steady state of flash (stage III). This work demonstrates situations where the BBR model alone does not accurately predict when a phase transformation will occur. We examine the model reactions of CuO reduction to Cu 2 O during stage II and Mn 2 O 3 reduction to Mn 3 O 4 in stage III. In CuO, highly resistive samples result in initially localized current flow, a stochastic process resulting in inhomogeneous heating and error in the BBR model during stage II. CuO reduction does not occur in constant heating rate experiments with 6.25 V/mm fields, even though the sample temperature momentarily exceeds the phase transformation temperature. Increased furnace heating to 950°C before application of a field is required to drive the transition. In Mn 2 O 3 , the calculated sample temperature of the gauge is less than the transformation temperature, but localized heating at the contact will exceed the transformation temperature, causing the transformation to propagate away from the electrode during stage III. This work demonstrates two forms of inhomogeneity (local, stochastic current flow, and local contact resistance) that result in a complex thermal profile of the sample. This profile should be interrogated to understand reaction kinetics, and can be beneficial when engineered.

The compound Ni4V3O10 forms a new structure type in the tetragonal space group P4/n. The material can be produced using solid-state synthesis in a narrow temperature range, and the structure was confirmed using X-ray and neutron powder diffraction data. The phase contains occupationally disordered Ni/V in tetrahedral, square pyramidal, and octahedral sites. Bond valence and neutron/X-ray co-refinements give evidence for three vanadium oxidation states (V^3+, V^4+, V^5+), making it distinct in the Ni-V-O system and placing it in a class of only nine other oxides with transition metals exhibiting three oxidation states. With a Néel temperature of 38 K and a Curie-Weiss parameter θ = -234 K, it displays frustrated antiferromagnetism, evidenced by a broad hump in the heat capacity below T_N. The structure has a percolating distorted rock-salt-like network, leading to strong superexchange, but square pyramidal linkages frustrate magnetic ordering. The magnetic structure is assumed to be incommensurate, as simple propagation vectors can be ruled out by powder neutron diffraction.