Soil Chemical Analysis

A wide array of forms of palladium has been utilized as precatalysts for Heck and Suzuki coupling reactions over the last 15 years. Historically, nearly every form of palladium used has been described as the active catalytic species. However, recent research has begun to shed light on the in situ transformations that many palladium precatalysts undergo during and before the catalytic reaction, and there are now many suggestions in the literature that narrow the scope of types of palladium that may be considered true “catalysts” in these coupling reactions. In this work, for each type of precatalyst, the recent literature is summarized and the type(s) of palladium that are proposed to be truly active are enumerated. All forms of palladium, including discrete soluble palladium complexes, solid-supported metal ligand complexes, supported palladium nano- and macroparticles, soluble palladium nanoparticles, soluble ligand-free palladium, and palladium-exchanged oxides are considered and reviewed here. A considerable focus is placed on solid precatalysts and on evidence for and against catalysis by solid surfaces vs. soluble species when starting with various precatalysts. The review closes with a critical overview of various control experiments or tests that have been used by authors to assess the homogeneity or heterogeneity of catalyst systems.

On the Nature of the Active Species in Palladium Catalyzed Mizoroki–Heck and Suzuki–Miyaura Couplings – Homogeneous or Heterogeneous Catalysis, A Critical Review

The potential of palladacycles: more than just precatalysts

Ethylene glycol (EG) is an important organic compound and chemical intermediate used in a large number of industrial processes (e.g. energy, plastics, automobiles, and chemicals). Indeed, owing to its unique properties and versatile commercial applications, a variety of chemical systems (e.g., catalytic and non-catalytic) have been explored for the synthesis of EG, particularly via reaction processes derived from fossil fuels (e.g., petroleum, natural gas, and coal) and biomass-based resources. This critical review describes a broad spectrum of properties of EG and significant advances in the prevalent synthesis and applications of EG, with emphases on the catalytic reactivity and reaction mechanisms of the main synthetic methodologies and applied strategies. We also provide an overview regarding the challenges and opportunities for future research associated with EG.

Ethylene glycol: properties, synthesis, and applications

Pd catalysis of C-C bond formations is briefly reviewed from the angle of nanoparticles (NPs) whether they are homogeneous or heterogeneous precatalysts and whether they are intentionally preformed or generated from a Pd derivative such as Pd(OAc)2. The most studied reaction is the Heck coupling of halogenoarenes with olefins that usually proceeds at high temperature (120-160 degrees C). Under such conditions, the PdII precursor is reduced to Pd0, forming PdNPs from which Pd atom leaching, subsequent to oxidative addition of the aryl halide onto the PdNP surface, is the source of very active molecular catalysts. Other C-C coupling reactions (Suzuki, Sonogashira, Stille, Negishi, Hiyama, Corriu-Kumada, Ullmann, and Tsuji-Trost) can also be catalyzed by species produced from preformed PdNPs. For catalysis of these reactions, leaching of active Pd atoms from the PdNPs may also provide a viable molecular mechanistic scheme. Thus, the term "PdNP catalysis of C-C coupling" used in this review refers to this function of PdNPs as precursors of catalytically active Pd species (i.e., the PdNPs are precatalysts of C-C coupling reactions).

Palladium nanoparticles as efficient green homogeneous and heterogeneous carbon-carbon coupling precatalysts: a unifying view.

A simple synthesis procedure for the immobilization of propyl thiol groups on silica is investigated using various concentrations of 3-mercapto propyl trimethoxy silane (3-MPTS) in the range of 5–40%. The thiol group functionalised silicas (SiO2–SH) were then oxidized to Bronsted sulphonic acid silica materials (SiO2–SO3H) using aqueous H2O2 as oxidizing agent. The surface structures of the functionalized catalysts were analyzed by a series of characterization techniques like elemental analysis, FTIR, TG-DTA, Surface area measurements, XPS, 13 C CP MAS NMR and 29 Si MAS NMR. The 13 C CP MAS NMR analyses confirm that disulphide species are not formed under the present preparation condition of catalysts. The acidity of the synthesized catalysts were further confirmed by the temperature programmed desorption of ammonia. The catalytic activity of the sulphonic acid functionalized silicas was evaluated in the liquid phase acetalization of ethyl acetoacetate with ethylene glycol and in the acetylation of anisole with acetic anhydride. The catalysts were found to be active in the acetalization reaction, which needs mild acidic sites, while the acetylation reactions gave lower activity, probably it needs stronger acid sites. A 30 wt.% SO3H loaded silica (SiO2–SO3H30) was recycled two times in the acetalization of ethyl acetoacetate and no major change in the conversion of EAA and selectivity to fructone is seen, which further argue against the possibility of leaching of the anchored sulphur containing species during reactions.

Silica functionalised sulphonic acid groups: synthesis, characterization and catalytic activity in acetalization and acetylation reactions

Synthesis, characterization, and catalytic activity of vanadium-incorporated, -grafted, and -immobilized mesoporous MCM-41 in the oxidation of aromatics

This article describes an in−depth follow−up to previous studies showing that an oil−methanol mixer prior to an RD reactor played an important role in enhancing the overall performance of the RD reactor system. An in−line static mixer was used for the purpose of providing initial mixing of the reactants, heating the mixture up to the desired operating temperature, and carrying out a substantial part of the transesterification reaction in the early stage. It performed three functions: a reactant mixer, a heat exchanger, and a pre−reactor. This article reports the systematic investigations of the pre−reactor performance by examining the effects of process variables on the process evaluating parameters, and the operating conditions for optimum operation. A wide range of results was observed under different operating conditions. The product yield was as high as 84.60% and as low as 1.63%. The soap formation was in the range of 2.80% to 10.37%. The feed molar ratio, reaction time, and catalyst concentration all contributed positively to the product yield and soap formation. Although an optimum condition produced a product yield of 80.46% and soap formation of 5.18% with a 1.33 min reaction time, the optimization should be based on the integration of the whole RD reactor system rather than a collection of individually optimized components. This study of the pre−reactor serves as an analysis tool for part of the RD reactor system.

Biodiesel Production

Vanadium-containing ordered mesoporous silicates: Does the silica source really affect the catalytic activity, structural stability, and nature of vanadium sites in V-MCM-41?

Oxidation of ethyl benzene and diphenyl methane over ordered mesoporous M-MCM-41 (M = Ti, V, Cr): Synthesis, characterization and structure–activity correlations

A.P. Singh

Papers

Silica functionalised sulphonic acid groups: synthesis, characterization and catalytic activity in acetalization and acetylation reactions

Synthesis, characterization, and catalytic activity of vanadium-incorporated, -grafted, and -immobilized mesoporous MCM-41 in the oxidation of aromatics

Biodiesel Production

Vanadium-containing ordered mesoporous silicates: Does the silica source really affect the catalytic activity, structural stability, and nature of vanadium sites in V-MCM-41?

Oxidation of ethyl benzene and diphenyl methane over ordered mesoporous M-MCM-41 (M = Ti, V, Cr): Synthesis, characterization and structure–activity correlations