Polymer Modification of Surface Electronic Properties of Electrocatalysts

Finding alternative ways to tailor the electronic properties of a catalyst to actively and selectively drive reactions of interest has been a growing research topic in the field of electrochemistry. In this Letter, we investigate the tuning of the surface electronic properties of electrocatalysts via polymer modification. We show that when a nickel oxide water oxidation catalyst is coated with polytetrafluoroethylene, stable Ni-CF _x bonds are introduced at the nickel oxide/polymer interface, resulting in shifting of the reaction selectivity away from the oxygen evolution reaction and toward hydrogen peroxide formation. It is shown that the electron-withdrawing character of the surface fluorocarbon molecule leaves a slight positive charge on the water oxidation intermediates at the adjacent active nickel sites, making their bonds weaker. The concept of modifying the surface electronic properties of an electrocatalyst via stable polymer modification offers an additional route to tune multipathway reactions in polymer/electrocatalyst environments, like with ionomer-modified catalysts or with membrane electrode assemblies.

CO 2 Hydrogenation to Methanol over Cd 4 /TiO 2 Catalyst: Insight into Multifunctional Interface

Supported metal catalysts have shown to be efficient for CO₂ conversion due to their multifunctionality and high stability. Herein, we have combined density functional theory calculations with microkinetic modeling to investigate the catalytic reaction mechanisms of CO₂ hydrogenation to CH₃OH over a recently reported catalyst of Cd₄/TiO₂. Calculations reveal that the metal‐oxide interface is the active center for CO₂ hydrogenation and methanol formation via the formate pathway dominates over the reverse water‐gas shift (RWGS) pathway. Microkinetic modeling demonstrated that formate species on the surface of Cd₄/TiO₂ is the relevant intermediate for the production of CH₃OH, and CH₂O^# formation is the rate‐determining step. These findings demonstrate the crucial role of the Cd‐TiO₂ interface for controlling the CO₂ reduction reactivity and CH₃OH selectivity.

Understanding the interaction between transition metal doping and ligand atoms of ZnS and ZnO monolayers to promote CO2 reduction reaction

Single-atom catalyst (SAC) obtained by doping a transition metal (TM) atom to stable monolayers is a promising way to improve CO2 reduction reaction (CRR) performance. In this work, we theoretically...

Active Sites in a Heterogeneous Organometallic Catalyst for the Polymerization of Ethylene

Heterogeneous derivatives of catalysts discovered by Ziegler and Natta are important for the industrial production of polyolefin plastics. However, the interaction between precatalysts, alkylaluminum activators, and oxide supports to form catalytically active materials is poorly understood. This is in contrast to homogeneous or model heterogeneous catalysts that contain resolved molecular structures that relate to activity and selectivity in polymerization reactions. This study describes the reactivity of triisobutylaluminum with high surface area aluminum oxide and a zirconocene precatalyst. Triisobutylaluminum reacts with the zirconocene precatalyst to form hydrides and passivates -OH sites on the alumina surface. The combination of passivated alumina and zirconium hydrides formed in this mixture generates ion pairs that polymerize ethylene.

Mechanistic investigation of benzene esterification by K2CO3/TiO2: the catalytic role of the multifunctional interface

Potassium carbonate dispersed over a defective TiO₂ support (K₂CO₃/TiO₂) is an efficient catalyst for benzene esterification with CO₂ and CH₃OH. Density functional theory calculations reveal that this unique catalytic reactivity originates from the cooperation of the Ti³⁺/K⁺ surface sites. The K₂CO₃ promotor steers the stabilization of surface intermediates thus preventing catalyst deactivation.

Defect sites on TiO₂ surface promote the direct carboxylation of benzene. The addition of K₂CO₃ destabilizes key surface intermediates and facilitates product evolution and propogation of the catalytic cycles.

Cyclomatrix Polyphosphazene Porous Networks with J-Aggregated Multiphthalocyanine Arrays for Dual-Modality Near-Infrared Photosensitizers

Here, we have developed a kind of cyclomatrix polyphosphazene with excellent photophysical properties and pursued their potential of being organic photosensitizers for dual-modality phototherapy. Briefly, hexachlorocyclophosphazene (HCCP) with D_{3 h} symmetry is adopted as a synthon to attach Zn(II) phthalocyanine (ZnPc) to form dendritic units that are covalently expanded into a soluble porous network through the nucleophilic substitution reaction. Molecular simulation reveals that the multi-ZnPc units around HCCP can be oriented in a side-by-side manner, leading to the remarkably red-shifted and intense absorbance in the near-infrared (NIR) region. To validate the potential in bioapplication, such ZnPc-based polyphosphazenes are assembled by incorporation of polyvinylpyrrolidone (PVP) to produce the uniform nanoparticles with aqueous dispersibility and biocompatibility. From the in vitro results, the PVP-stabilized photosensitizing nanoparticles can undergo the photothermal/photodynamic processes to concurrently generate heat and singlet oxygen for efficiently killing cancer cells upon exposure to a single-bandwidth NIR laser (785 nm). Compared with the known organic photosensitizers, cyclomatrix polyphosphazene would be a promising platform to configure a diversity of reticular arrays with dense and oriented arrangement of dye molecules, leading to their largely enhanced photophysical and photochemical properties.

Towards operando computational modeling in heterogeneous catalysis

An increased synergy between experimental and theoretical investigations in heterogeneous catalysis has become apparent during the last decade. Experimental work has extended from ultra-high vacuum and low temperature towards operando conditions. These developments have motivated the computational community to move from standard descriptive computational models, based on inspection of the potential energy surface at 0 K and low reactant concentrations (0 K/UHV model), to more realistic conditions. The transition from 0 K/UHV to operando models has been backed by significant developments in computer hardware and software over the past few decades. New methodological developments, designed to overcome part of the gap between 0 K/UHV and operando conditions, include (i) global optimization techniques, (ii) ab initio constrained thermodynamics, (iii) biased molecular dynamics, (iv) microkinetic models of reaction networks and (v) machine learning approaches. The importance of the transition is highlighted by discussing how the molecular level picture of catalytic sites and the associated reaction mechanisms changes when the chemical environment, pressure and temperature effects are correctly accounted for in molecular simulations. It is the purpose of this review to discuss each method on an equal footing, and to draw connections between methods, particularly where they may be applied in combination.

Oxotitanium-porphyrin for selective catalytic reduction of NO by NH3: a theoretical mechanism study

Nitric oxide reduction catalyzed by oxotitanium-porphyrin.

Mechanistic study of NO oxidation on Cr–phthalocyanine: theoretical insight

A mechanistic investigation by DFT reveals that Cr–phthalocyanine is a promising catalyst for NO oxidation at low temperatures.

A Cr-phthalocyanine monolayer as a potential catalyst for NO reduction investigated by DFT calculations

The reaction mechanism of nitric oxide (NO) reduction to nitrous oxide (N₂O) and N₂ catalyzed by Cr-phthalocyanine sheet (CrPc) was investigated using periodic density functional theory (DFT).

Mechanistic insight into the selective catalytic reduction of NO by NH3 over low-valent titanium-porphyrin: a DFT study

The theoretical study shows that Ti-porphyrin has potential as an alternative catalyst for NH₃-SCR of NO.