CO2 Hydrogenation to Methanol over Cd4/TiO2 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 the CO2 reduction reaction.

Single-atom catalysts (SACs) obtained by doping transition metal (TM) atoms into stable monolayers are a promising way to improve the CO2 reduction reaction (CRR) performance. In this work, we theoretically investigated the effect of ligand atoms around the doped TM (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) in ZnO and ZnS for promoting the CRR performance. We found that the ligand atoms around the TM can influence its oxidation state and the electronic properties of the SACs, thus affecting their CRR activity. Due to the smaller charge transfer between the TM and substrate for TM-ZnS compared to TM-ZnO, the TM binding is weaker for the former. In addition, the more negatively charged oxygen ligand atoms in TM-ZnO interact with reaction intermediates, resulting in CRR products with less electron transfer. Pristine ZnS and ZnO monolayers can produce HCOOH but require a high limiting potential (UL) of about -1.2 V. Doping with TMs can reduce UL compared to the pristine surface. At the same time, the ligand can alter the preferred CRR pathway and product selectivity. We found that Mn-ZnS is selective to the CH4 product with a UL of only -0.29 V, which is a nearly 1 V improvement in the UL compared to ZnS.

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.

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.

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 D3 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.

Effects of amine organic groups as lattice in ZSM-5 on the hydrolysis of dimethyl ether.

The effects of doping amine to ZSM-5 on its catalytic activity for hydrolysis of dimethyl ether (DME) have been studied theoretically using Density Functional Theory with the embedded cluster ONIOM(M06/6-31G(d,p):UFF) model. Doping by amine to ZSM-5 yields two new active centers, namely the protonated Z[NH2] and non-protonated Z[NH] amine sites in addition to the normal Brønsted acid Z[OH] site. The reaction has two possible stepwise and concerted channels. The stepwise channel consists of two elementary steps; (i) the demethylation followed by (ii) the hydrolysis while the concerted channel involves in the demethylation and hydrolysis in a single step. We found that the reaction favors to proceed via the concerted channel at all three active centers. The results predict that the Z[OH] shows the best catalytic performance for the studied reaction. The Z[NH2] is not catalytically active due to the activation barriers are extremely high for both stepwise and concerted pathways. The demethylation step is energetically favorable over the Z[NH] site, however, the product methylamonium surface intermediate is too stable to be further converted to methanol.