Ultrasound- and microwave-assisted preparation of lead-free palladium catalysts: effects on the kinetics of diphenylacetylene semi-hydrogenation

The effect of environmentally benign enabling technologies such as ultrasound and microwaves on the preparation of the lead-free Pd catalyst has been studied. A one-pot method of the catalyst preparation using ultrasound-assisted dispersion of palladium acetate in the presence of the surfactant/capping agent and boehmite support produced the catalyst containing Pd nanoparticles and reduced the number of pores larger than 4 nm in the boehmite support. This catalyst demonstrated higher activity and selectivity. The comparison of kinetic parameters for diphenylacetylene hydrogenation showed that the catalyst obtained by using the one-pot method was seven times as active as a commercial Lindlar catalyst and selectivity towards Z-stilbene was high. Our work also illustrated that highly selective Pd/boehmite catalysts can be prepared through ultrasound-assisted dispersion and microwave-assisted reduction in water under hydrogen pressure without any surfactant

Controlling Hydrocarbon (De)Hydrogenation Pathways with Bifunctional PtCu Single-Atom Alloys

The conversions of surface-bound alkyl groups to alkanes and alkenes are important steps in many heterogeneously catalyzed reactions. On the one hand, while Pt is ubiquitous in industry because of its high activity toward C-H activation, many Pt-based catalysts tend to overbind reactive intermediates, which leads to deactivation by carbon deposition and coke formation. On the other hand, Cu binds intermediates more weakly than Pt, but activation barriers tend to be higher on Cu. We examine the reactivity of ethyl, the simplest alkyl group that can undergo hydrogenation and dehydrogenation via β-elimination, and show that isolated Pt atoms in Cu enable low-temperature hydrogenation of ethyl, unseen on Cu, while avoiding the decomposition pathways on pure Pt that lead to coking. Furthermore, we confirm the predictions of our theoretical model and experimentally demonstrate that the selectivity of ethyl (de)hydrogenation can be controlled by changing the surface coverage of hydrogen

The Reduction of Alkynes over Pd-based Catalyst Materials-A Pathway to Chemical Synthesis

Many reactions, including selective hydrogenation of alkynes, take place on solid surfaces. These reactions are vital in many areas of industry including the manufacture of polymers and fine chemicals such as vitamins, fragrances, and drugs. The choice of a catalyst is a trade-off between activity, selectivity and costs. Palladium-based heterogeneous catalysts are traditionally used for these processes as they provide the activation of hydrogen at room temperatures and offers reasonable selectivity, but these catalysts have a number of practical drawbacks. This review discusses recent research work in the selective hydrogenation of alkynes on palladium-based catalysts, emphasises the mechanism and catalytic materials and important applications including alkyne removal from gas-phase alkene precursors for polymer synthesis and liquid phase selective hydrogenation for the synthesis of fine chemicals. Langmuir-Hinshelwood reaction kinetic models, reaction intermediates, formation of carbonaceous layer, the nature of active sites and the effects of reversible and irreversible adsorbates over Pd surface are discussed as well as the factors affecting catalyst activity and selectivity and how these can be optimised in synthetic protocols for these reactions

Palladium-bismuth intermetallic and surface-poisoned catalysts for the semi-hydrogenation of 2-methyl-3-butyn-2-ol

The effects of poisoning of Pd catalysts with Bi and annealing in a polyol (ethylene glycol) were studied on the semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY). An increase in the Pd:Bi ratio from 7 to 1 in the Bi-poisoned catalysts decreased the hydrogenation activity due to blocking of active sites, but increased maximum alkene yield from 91.5% for the Pd catalyst to 94–96% for all Bi-poisoned Pd catalysts, by decreasing the adsorption energy of alkene molecules and suppressing the formation of β-hydride phase. Annealing of the catalysts induced the formation of intermetallic phases and decreased its activity due to sintering of the catalytic particles and low activity of intermetallic compounds. Langmuir–Hinshelwood kinetic modelling of the experimental data showed that poisoning of Pd with Bi changed the relative adsorption constants of organic species suggesting ligand effects at high Bi content

Butene Isomerization on Palladium Surfaces: Time-Dependent Monte Carlo Studies

A new time-dependent Monte Carlo approach, tdMC, is presented. This allows one to manage the quantum-chemical information relating to surface catalytic processes and rationalize, with atomistic dynamical perspectives, the corresponding reaction mechanism by providing descriptors that can be compared with experimentally obtained data. The approach, which falls into the more general microkinetic paradigm, is strictly self-consistent as it exploits information framed in just one computational method based on the density functional theory. The results simulated by the tdMC algorithm concern the isomerization of but-1-ene to cis- and trans-but-2-ene on Pd surfaces. This reaction was chosen mainly to focus on the development and implementation of the model as well as to point out the characteristics of the code and the soundness of the approach. In order to reach these goals, the simulated findings were compared to related experimental and computational literature data. From the study, it clearly emerges that the tdMC approach, although conceptually very straightforward and simple, is flexible enough to pinpoint the main characteristics of the reaction, which is just seemingly elementary and conversely governed by a complex mechanism involving, besides isomerization, even hydrogenation and dehydrogenation processes. Noticeably, new insights into the title reaction were also provided by the proposed approach

Adsorbate-Induced Structural Evolution of Pd Catalyst for Selective Hydrogenation of Acetylene

ACKNOWLEDGMENT: This work was financially supported by National Natural Science Foundation of China (21908002), project funded by China Postdoctoral Science Foundation (2019M660416, 2020T130045) and the Fundamental Research Funds for the Central Universities (buctrc201921, JD2004, XK1802-6). We would like to thank the UK catalysis Hub for help collecting the XAS.Peer reviewedPostprin

Ethene dimerization on zeolite-hosted Ni ions : reversible mobilization of the active site

The active site in ethene oligomerization catalyzed by Ni-zeolites is proposed to be a mobile Ni(II) complex, based on density functional theory-based molecular dynamics (DFT-MD) simulations corroborated by continuous-flow experiments on Ni-SSZ-24 zeolite. The results of the simulations at operating conditions show that ethene molecules reversibly mobilize the active site as they exchange with the zeolite as ligands on Ni during reaction. Microkinetic modeling was conducted on the basis of free-energy profiles derived with DFT-MD for oligomerization on these mobile [(ethene)(2)-Ni-alkyl](+) species. The model reproduces the experimentally observed high selectivity to dimerization and indicates that the mechanism is consistent with the observed second-order rate dependence on ethene pressure

Selectivity of the Lindlar catalyst in alkyne semi-hydrogenation: a direct liquid-phase adsorption study

We study the alkyne semi-hydrogenation selectivity over Pd and Lindlar catalyst with liquid phase adsorption. The results indicate that there are strongly-adsorbing alkyne and alkene sites; alkenes react non-selectively over the alkene adsorption sites. DFT studies indicate that the non-selective sites are low-coordination Pd atoms in the nanoparticles

Catalytic Transfer Hydrogenation Reactions of Lipids

Catalytic transfer hydrogenation (CTH) of lipids was investigated using 2-propanol as hydrogen donor for producing liquid hydrocarbons, e.g. jet fuels. The main sources of lipids selected in this study were waste cooking oil (WCO) and oil-laden algae-derived biofuel intermediate (BI). Two different catalysts were employed in this study, namely activated carbon and trimetallic-doped zeolite. The CTH reaction was between WCO and 2-propanol in a continuous flow reactor over a packed-bed activated carbon at near atmospheric pressure. Results revealed a high level of alkenes and aromatics compounds, which are not stable and are not environmentally unfriendly. To reduce these compounds in the liquid fuel, trimetallic catalyst was prepared and the reaction was by optimizing the reaction variables (temperature, pressure, weight hourly space velocity, and oil-2-propanol ratio). Results from the second study were better than that of the first, as the level of aromatics and alkenes was lower in the second study. However, the amount of branched and cyclo-alkanes (high octane rating compounds) was insignificant. Lipids from algae-derived oil-laden BI were extracted by 2-propanol and without evaporation of alcohol; the pregnant 2-propanol was subjected to CTH over the prepared trimetallic catalyst in a batch reactor. The liquid fuel product from this third study produced significant branched and cyclo-alkanes (serendipity). Finally, technoeconomic analysis (TEA) and life cycle assessment (LCA) of CTH reaction were conducted. The results were compared, with a conventional hydroprocessed renewable jet fuels (HRJ) process. Results showed that the economic performance of CTH was lower than that of HRJ, due to the large volume of 2-propanol employed in the CTH. However, the environmental performance of CTH was very impressive, compared to that of HRJ. Chapter 1 of this study describes the rationale for selecting WCO and 2-propanol as the potential hydrogen donor. In Chapter 2, 2-propanol was used the react with waste cooking oil by considering four reaction parameters: temperature, oil flow rate, WHSV, and pressure. Finally, the kinetics of the reaction were ascertained, in order to estimate reaction order, activation energy, and kinetic rate constant. Chapter 3 employed commercial catalyst doped with transition metals which catalyzed the reaction between waste cooking oil and 2-propanol. Optimization of the reaction was studied by varying temperature, WHSV, pressure, and oil-2-propanol ratio. The percent of transition metal employed remained constant. Chapter 4, on the other hand, explored the possibility of using oil-laden biofuel intermediate from flash hydrolyzed algae. The purpose was to utilize 2-propanol as oil extract and hydrogen donor in CTH reaction of the oil. Finally, Chapter 5 thoroughly discussed the technoeconomic and environmental performance of the CTH reaction of waste cooking oil and 2-propanol