4 research outputs found
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<sup>–2</sup> in 0.5 M H<sub>2</sub>SO<sub>4</sub> 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<sup>–2</sup>. 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<sup>–2</sup> 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/TiO<sub>2</sub> 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-NOsÂ(6 nm) was 2.6 times as high as that of Pd-NCsÂ(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 O<sub>2</sub> hydrogenation to
produce peroxide
Elucidating Ionic Liquid Environments That Affect the Morphology of TiO<sub>2</sub> Nanocrystals: A DFT+<i>D</i> Study
Using ionic liquids as controlling
agents is known to effectively
affect the morphologies of TiO<sub>2</sub> 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]ÂBr) adsorption on the low-index TiO<sub>2</sub> facets,
and the equilibrium crystal shape of TiO<sub>2</sub> 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