Liquid-Phase Dehydration of Glycerol to Acrolein with ZSM-5-Based Catalysts in the Presence of a Dispersing Agent

Liquid-phase dehydration of glycerol to acrolein was investigated with solid acid catalysts, including H-ZSM-5, H₃PO₄-modified H-ZSM-5, H₃PW₁₂O₄₀·14H₂O and Cs_2.5H_0.5PW₁₂O₄₀, in the presence of sulfolane ((CH₂)₄SO₂) as a dispersing agent under atmospheric pressure N₂ in a batch reactor. High weak-acidity H-ZSM-5, high temperatures and high-boiling-point sulfolane improved the activity and selectivity for the production of acrolein through suppressing the formation of polymers and coke and promoting the diffusion of glycerol and products. Brønsted acid sites were soundly demonstrated to be responsible for dehydration of glycerol to acrolein by infrared spectroscopy of pyridine adsorption. Brønsted weak acid sites favored the selectivity to acrolein. Combined catalytic and temperature-programmed desorption of ammonia studies revealed that the selectivity to acrolein increased as the weak-acidity increased over the ZSM-5-based catalysts. The ZSM-5-based catalysts produced a higher selectivity to acrolein, while the heteropolyacids resulted in a higher selectivity to polymers and coke.

Stable catalysis of neutral silica-supported potassium lactate for vapour-phase dehydration of lactic acid to acrylic acid – Critical role of support

We have deeply investigated KNO3-derived silica-supported potassium lactate catalysts for vapour-phase dehydration of lactic acid (LA) to acrylic acid (AA) by catalytic testing, IR spectroscopic monitoring, ammonia temperature-programmed desorption, isopropyl...

Strong Metal-Support Interaction for 2D Materials: Application in Noble Metal/TiB2 Heterointerfaces and their Enhanced Catalytic Performance for Formic Acid Dehydrogenation

Strong metal-support interaction (SMSI) is a phenomenon commonly observed on heterogeneous catalysts. Here, direct evidence of SMSI between noble metal and 2D TiB₂ supports is reported. The temperature-induced TiB₂ overlayers encapsulate the metal nanoparticles, resulting in core-shell nanostructures that are sintering-resistant with metal loadings as high as 12.0 wt%. The TiO_x -terminated TiB₂ surfaces are the active sites catalyzing the dehydrogenation of formic acid at room temperature. In contrast to the trade-off between stability and activity in conventional SMSI, TiB₂ -based SMSI promotes catalytic activity and stability simultaneously. By optimizing the thickness and coverage of the overlayer, the Pt/TiB₂ catalyst displays an outstanding hydrogen productivity of 13.8 mmol g^-1 _cat h^-1 in 10.0 m aqueous solution without any additive or pH adjustment, with >99.9% selectivity toward CO₂ and H₂ . Theoretical studies suggest that the TiB₂ overlayers are stabilized on different transition metals through an interplay between covalent and electrostatic interactions. Furthermore, the computationally determined trends in metal-TiB₂ interactions are fully consistent with the experimental observations regarding the extent of SMSI on different transition metals. The present research introduces a new means to create thermally stable and catalytically active metal/support interfaces for scalable chemical and energy applications.

Materializing efficient methanol oxidation via electron delocalization in nickel hydroxide nanoribbon

Achieving a functional and durable non-platinum group metal-based methanol oxidation catalyst is critical for a cost-effective direct methanol fuel cell. While Ni(OH)₂ has been widely studied as methanol oxidation catalyst, the initial process of oxidizing Ni(OH)₂ to NiOOH requires a high potential of 1.35 V vs. RHE. Such potential would be impractical since the theoretical potential of the cathodic oxygen reduction reaction is at 1.23 V. Here we show that a four-coordinated nickel atom is able to form charge-transfer orbitals through delocalization of electrons near the Fermi energy level. As such, our previously reported periodically arranged four-six-coordinated nickel hydroxide nanoribbon structure (NR-Ni(OH)₂) is able to show remarkable methanol oxidation activity with an onset potential of 0.55 V vs. RHE and suggests the operability in direct methanol fuel cell configuration. Thus, this strategy offers a gateway towards the development of high performance and durable non-platinum direct methanol fuel cell.

Synthesis of Mesoporous Copper Aluminosilicate Hollow Spheres for Oxidation Reactions

Hollow functional metal silicate materials have received the most interest due to their large inner space, permeable and functional shell, lighter density, and better use of material compared to their solid counterparts. While tremendous success has been made in the synthesis of individual metal silicates with uniform morphology, the synthesis of multiphase hollow silicates has not been explored yet, although their direct applications could be promising. In this study, mesoporous aluminosilicate spheres (MASS) are transformed to submicrometer copper aluminosilicate hollow spheres (CASHS) via a one-pot hydrothermal process. CASHS has a hollow interior with Cu-Al-Si thorn-like moieties in a lamellar structure on its outer shell. The structure and morphology of CASHS are unique and different from the previously reported tubular copper silicates that are emanated from Stöber silica spheres. Herein, we also demonstrate that the extent of hollowing in CASHS can be attained by controlling the aluminum content of pristine MASS, highlighting the existence of parameters for in situ controlling the shell thickness of hollow materials. The application of CASHS as a potential heterogeneous catalyst has been directed to important oxidation processes such as olefin oxidation and the advanced oxidation process (AOP). In cyclohexene oxidation, for instance, high selectivity to cyclohex-2-en-1-one is achieved under moderate conditions using tert-butyl hydroperoxide as the oxidant. CASHS is a robust heterogeneous catalyst and recyclable for this reaction. CASHS-derived catalysts also favor AOP and enhance the removal of cationic dyes together with H₂O₂ through an adsorption-degradation process.

Dual catalyst system for selective vinyl chloride production via ethene oxychlorination

A dual system featuring ZrO₂-supported CeO₂ and Ca-doped Al₂O₃ catalysts enables the direct production of vinyl chloride via ethene oxychlorination.

In Situ-Generated Supported Potassium Lactate: Stable Catalysis for Vapor-Phase Dehydration of Lactic Acid to Acrylic Acid

We have studied unsupported, silica gel- and amorphous silica-alumina-supported catalysts derived from K salts for the vapor-phase dehydration of lactic acid (LA) to acrylic acid (AA). A catalytic study shows that the supported catalysts improve the activity and selectivity for the production of AA and decrease the selectivity for the production of propionic acid (PA). The silica-alumina-supported catalysts remain fairly stable in the catalytic performance during 90 h of reaction. The IR spectroscopic characterization combined with the catalytic study demonstrates that potassium lactate (C₃H₅KO₃) in situ generated from LA and a K salt is an important reaction intermediate for the production of AA and the catalytic stability is associated with the chemical stability of C₃H₅KO₃ and the activity for the regeneration of C₃H₅KO₃ in the catalytic cycle. On silica-alumina, C₃H₅KO₃ is well stabilized and smoothly regenerated during the reaction, leading to the good catalytic stability. This work suggests for the first time that lactate salt acts as the true catalytic active species for the dehydration of LA to AA. We also propose a predominant reaction pathway for the vapor-phase dehydration of LA to AA with K salt catalyst systems.

Identifying the Origin and Contribution of Surface Storage in TiO2 (B) Nanotube Electrode by In Situ Dynamic Valence State Monitoring

Fundamental insight into the surface charging mechanism of TiO2 (B) nanomaterials is limited due to the complicated nature of lithiation behavior, as well as the limitations of available characterization tools that can directly probe surface charging process. Here, an in situ approach is reported to monitor the dynamic valence state of TiO2 (B) nanotube electrodes, which utilizes in situ X-ray absorption spectroscopy (XAS) to identify the origin and contribution of surface storage. A real-time correlation is elucidated between the rate-dependent electrode performance and dynamic Ti valence-state change. A continuous Ti valence state change is directly observed through the whole charging/discharging process regardless of charging rates, which proves that along with the well-known non-faradaic reaction, the surface charging process also originates from a faradaic reaction. The quantification of these two surface storage contributions at different charging rates is further realized through in situ dynamic valence state monitoring combined with traditional cyclic voltammetry measurement. The methodology reported here can also be applied to other electrode materials for the real-time probing of valence state change during electrochemical reactions, the quantification of the faradaic and non-faradaic reactions, and the eventual elucidation of electrochemical surface charging mechanisms.

Crystal Phase and Architecture Engineering of Lotus-Thalamus-Shaped Pt-Ni Anisotropic Superstructures for Highly Efficient Electrochemical Hydrogen Evolution

The rational design and synthesis of anisotropic 3D nanostructures with specific composition, morphology, surface structure, and crystal phase is of significant importance for their diverse applications. Here, the synthesis of well-crystalline lotus-thalamus-shaped Pt-Ni anisotropic superstructures (ASs) via a facile one-pot solvothermal method is reported. The Pt-Ni ASs with Pt-rich surface are composed of one Ni-rich "core" with face-centered cubic (fcc) phase, Ni-rich "arms" with hexagonal close-packed phase protruding from the core, and facet-selectively grown Pt-rich "lotus seeds" with fcc phase on the end surfaces of the "arms." Impressively, these unique Pt-Ni ASs exhibit superior electrocatalytic activity and stability toward the hydrogen evolution reaction under alkaline conditions compared to commercial Pt/C and previously reported electrocatalysts. The obtained overpotential is as low as 27.7 mV at current density of 10 mA cm^-2 , and the turnover frequency reaches 18.63 H₂ s^-1 at the overpotential of 50 mV. This work provides a new strategy for the synthesis of highly anisotropic superstructures with a spatial heterogeneity to boost their promising application in catalytic reactions.

A Highly Efficient Oxygen Evolution Catalyst Consisting of Interconnected Nickel-Iron-Layered Double Hydroxide and Carbon Nanodomains

In this work, a one-pot solution method for direct synthesis of interconnected ultrafine amorphous NiFe-layered double hydroxide (NiFe-LDH) (<5 nm) and nanocarbon using the molecular precursor of metal and carbon sources is presented for the first time. During the solvothermal synthesis of NiFe-LDH, the organic ligand decomposes and transforms to amorphous carbon with graphitic nanodomains by catalytic effect of Fe. The confined growth of both NiFe-LDH and carbon in one single sheet results in fully integrated amorphous NiFe-LDH/C nanohybrid, allowing the harness of the high intrinsic activity of NiFe-LDH due to (i) amorphous and distorted LDH structure, (ii) enhanced active surface area, and (iii) strong coupling between the active phase and carbon. As such, the resultant NiFe-LDH/C exhibits superior activity and stability. Different from postdeposition or electrostatic self-assembly process for the formation of LDH/C composite, this method offers one new opportunity to fabricate high-performance oxygen evolution reaction and possibly other catalysts.

Selective conversion of lactic acid to acrylic acid over alkali and alkaline-earth metal co-modified NaY zeolites

A high AA selectivity of 84% was achieved through an environmentally friendly and sustainable catalytic process.

Lanthanum oxycarbonate modified Cu/Al2O3 catalysts for selective hydrogenolysis of glucose to propylene glycol: base site requirements

Moderate and strong base sites play a key role in glucose hydrogenolysis over bifunctional Cu–La₂O₂CO₃/Al₂O₃ catalysts.

The role of metal–support interaction for CO-free hydrogen from low temperature ethanol steam reforming on Rh–Fe catalysts

Effect of metal–support interaction on the generation of Rh–Fe_xO_y active sites is investigated via various in situ techniques.

Dehydration of lactic acid to acrylic acid over lanthanum phosphate catalysts: the role of Lewis acid sites

Lewis acidic sites on the surface of lanthanum phosphate nano-rods play a crucial role on the catalytic dehydration of lactic acid to acrylic acid.

XAFCA: a new XAFS beamline for catalysis research

A new X-ray absorption fine-structure (XAFS) spectroscopy beamline for fundamental and applied catalysis research, called XAFCA, has been built by the Institute of Chemical and Engineering Sciences, and the Singapore Synchrotron Light Source. XAFCA covers the photon energy range from 1.2 to 12.8 keV, making use of two sets of monochromator crystals, an Si (111) crystal for the range from 2.1 to 12.8 keV and a KTiOPO4 crystal [KTP (011)] for the range between 1.2 and 2.8 keV. Experiments can be carried out in the temperature range from 4.2 to 1000 K and pressures up to 30 bar for catalysis research. A safety system has been incorporated, allowing the use of flammable and toxic gases such as H2 and CO.

Nano Ru catalysts supported on carbon nanotubes for cellobiose conversion to sugar alcohols: effects of CNT channel size

The catalytic activity of a Ru/CNT-in sample was enhanced with the decrease of the CNT inner diameter and it was much higher than that of Ru/CNTs-out.

C–O cleavage of aromatic oxygenates over ruthenium catalysts. A computational study of reactions at step sites

C–O scissions of catecholate and phenolate on stepped Ru surfaces have accessible barriers. Computational results illustrate that benzene formation in the hydrodeoxygenation of aromatics over Ru occurs at step sites.

Catalytic oxidation of cellobiose over TiO2 supported gold-based bimetallic nanoparticles

A series of TiO₂ supported Au–M (M = Cu, Co, Ru and Pd) bimetallic catalysts were tested for cellobiose oxidation. Cu–Au and Ru–Au provided excellent gluconic acid selectivity’s, although via contrasting mechanism.