Highly Active and Stable Catalysts of Phytic Acid-Derivative Transition Metal Phosphides for Full Water Splitting

Application of transition metal phosphide (TMP) catalysts for full water splitting has great potential to help relieve the energy crisis. Various methods have been investigated to obtain high catalytic activity, but the use of electronic structure regulation by incorporation of different elements is of particular simplicity and significance for development of a universal TMP synthesis method. We herein describe a novel approach for fabricating a series of TMPs by pyrolyzing phytic acid (PA) cross-linked metal complexes. The introduction of oxygen atoms into TMPs not only enhanced their intrinsic electrical conductivity, facilitating electron transfer, but activated active sites via elongating the M–P bond, favoring the hydrogen evolution reaction (HER) or oxygen evolution reaction (OER). MoP exhibited relative low HER overpotentials of 118 mV and 93 mV while supporting a current density of 20 mA·cm^–2 in 0.5 M H₂SO₄ and 1 M KOH electrolytes, respectively. When CoP was applied as a catalyst for OER, only 280 mV overpotential was required to reach current density of 10 mA·cm^–2. Additionally, PA-containing precursors enabled intimate embedding of TMPs onto a flexible substrate surface (carbon cloth), so that electron injection from substrate and transport to the active sites was facilitated. Remarkably, an alkaline electrolyzer was able to achieve a current density of 40 mA·cm^–2 at the low voltage of 1.6 V, demonstrating its potential for practical overall water splitting without the use of noble metals

Selective Catalytic Hydrogenolysis of Carbon–Carbon σ Bonds in Primary Aliphatic Alcohols over Supported Metals

The selective scission of chemical bonds is always of great significance in organic chemistry. The cleavage of strong carbon–carbon σ bonds in the unstrained systems remains challenging. Here, we report the selective hydrogenolysis of carbon–carbon σ bonds in primary aliphatic alcohols catalyzed by supported metals under relatively mild conditions. In the case of 1-hexadecanol hydrogenolysis over Ru/TiO₂ as a model reaction system, the selective scission of carbon–carbon bonds over carbon–oxygen bonds is observed, resulting in <i>n</i>-pentadecane as the dominant product with a small quantity of <i>n</i>-hexadecane. Theoretical calculations reveal that the 1-hexadecanol hydrogenolysis on flat Ru (0001) undergoes two parallel pathways: i.e. carbon–carbon bond scission to produce <i>n</i>-pentadecane and carbon–oxygen bond scission to produce <i>n</i>-hexadecane. The removal of adsorbed CO on a flat Ru (0001) surface is a crucial step for the 1-hexadecanol hydrogenolysis. It contributes to the largest energy barrier in <i>n</i>-pentadecane production and also retards the rate for <i>n</i>-hexadecane production by covering the active Ru (0001) surface. The knowledge presented in this work has significance not just for a fundamental understanding of strong carbon–carbon σ bond scission but also for practical biomass conversion to fuels and chemical feedstocks

Facet Effect of Single-Crystalline Pd Nanocrystals for Aerobic Oxidation of 5‑Hydroxymethyl-2-furfural

Single-crystalline Pd nanocrystals enclosed by {111} or {100} facets with controllable sizes were synthesized and originally employed as catalysts in the aerobic oxidation of 5-hydroxymethyl-2-furfural (HMF). The experimental results indicated that the particle size and exposed facet of Pd nanocrystals could obviously influence their catalytic performance. The size-dependent effect of Pd nanocrystals in this reaction could only be derived from the different Pd dispersions. Therefore, the facet effect of Pd nanocrystals was first investigated in this work through experimental and theoretical approaches. It was found that Pd-NOs enclosed by {111} facets were more efficient than Pd-NCs enclosed by {100} facets for the aerobic oxidation of HMF, especially for the oxidation step from 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) toward 5-formyl-2-furancarboxylic acid (FFCA). The TOF value of Pd-NOs­(6 nm) was 2.6 times as high as that of Pd-NCs­(7 nm) and 5.2 times higher than that of commercial Pd/C catalyst for HMF oxidation. Through density functional theory (DFT) calculations, the notably enhanced catalytic performance of Pd-NOs could be mainly attributed to the lower energy barrier in the alcohol oxidation step (from HMFCA to FFCA) and higher selectivity for O₂ hydrogenation to produce peroxide

Elucidating Ionic Liquid Environments That Affect the Morphology of TiO₂ Nanocrystals: A DFT+<i>D</i> Study

Using ionic liquids as controlling agents is known to effectively affect the morphologies of TiO₂ crystals. To obtain a profound understanding of this observation, density functional theory calculations with inclusion of Grimme treatment of the dispersion forces (DFT+<i>D</i>) have been performed to study a typical ionic liquid 1-ethyl-3-methylimidazolium bromide ([Emim]­Br) adsorption on the low-index TiO₂ facets, and the equilibrium crystal shape of TiO₂ has been predicted using Wulff’s rule. [Emim]Br is found to adsorb most strongly on (110) for rutile and (100) for anatase. The gap of surface energy shows an obvious increase after [Emim]Br adsorption, especially, between (101) and (001) for anatase and also between (110) and (001) for rutile. This gap variation results in increasing the (100) facet exposure of anatase, and an increase in the length-to-diameter ratio of rutile nanocrystals, which is verified by our experiments. This study is meaningful to gain further understanding of how ionic liquids achieve shape-controlled nanocrystals synthesis by turning surface chemistry, which will push a valuable step toward the ultimate goal, controlling synthesis of inorganic nanomaterials