Controlling the activity of an immobilised molecular catalyst by Lewis acidity tuning of the support

Tuning Polyethylene Molecular Weight Distributions Using Catalyst Support Composition

“…The Lewis acidity of the support has been previously shown to influence how MAO and aluminum alkyls bind to protic supports, while interactions with the support may influence the stability of MAO species, the barrier to activation, and the cation–anion separation for MAO/metallocene ion pairs . Recently, we demonstrated that the Lewis acidity of an LDO surface can increase the productivity of (EBI)­ZrCl 2 immobilized using MAO by influencing the ion-pairing . This Lewis acidity can be shown by a change in the absorption of NH 3 , from binding solely via hydrogen bonds (“type A” sites) to incorporating both a hydrogen bond and a dative bond (“type B” sites, see Figure ).…”

“…However, we can assume that these changes influence the ion pairs formed when the zirconocene [(EBI)­ZrCl 2 ] reacts with the support. Different ion pairs will have not only different rates of reaction with the scavenger (TiBA) but also differing activities . Interestingly, the nickel-containing supports display enough chemical heterogeneity to produce ion pairs, which produce a high molecular weight polyethylene as well as new sites that readily react with TiBA to give a low molecular weight fraction.…”

“…70 Recently, we demonstrated that the Lewis acidity of an LDO surface can increase the productivity of (EBI)ZrCl 2 immobilized using MAO by influencing the ion-pairing. 71 This Lewis acidity can be shown by a change in the absorption of NH 3 , from binding solely via hydrogen bonds ("type A" sites) to incorporating both a hydrogen bond and a dative bond ("type B" sites, see Figure 8). 72 Upon comparison of the TPD profiles of Ni x (Mg 2−x )Al LDO, it is apparent that there is a dramatic change in the Lewis acidity of the supports.…”

Syntheses of Silylene-Bridged Thiophene-Fused Cyclopentadienyl ansa-Metallocene Complexes for Preparing High-Performance Supported Catalyst

“…When a homogeneous catalyst is injected, as dissolved, into a slurry-or gas-phase reactor, the shape and size of the generated polymer particles are irregularly uncontrolled, making stable operation impossible (termed 'fouling') as well as causing low productivity due to low bulk density. Because a large portion of PE and PP is produced by the slurry and gas-phase processes, high-performance supported catalysts are essential in the industrial sector [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26].…”

Construction of Frustrated Lewis Pair Sites in CeO2–C/BiVO4 for Photoelectrochemical Nitrate Reduction

“…Song et al constructed the CeO x heterostructure and demonstrated that CoP/CeO x could adjust the electronic structure to enhance the intrinsic activity and promote electron transfer, thus achieving high catalytic activity. , However, the collaborative controllability of chemisorption and catalytic activity is relatively limited in the traditional configuration of heterostructures because it is difficult to achieve the targeted design of surface sites. − In 2006, Stephan et al demonstrated that the small molecules could be efficiently reacted at the surface sites that were composed of sterically hindered Lewis acids (LAs) and Lewis bases (LBs), and these kinds of sites were known as “frustrated Lewis pairs (FLPs)” . LAs and LBs can accept and donate the electrons over small molecules, thereby realizing the chemical bond cleavage, which contributes to the optimization of catalysts. − For example, Huang’s group successfully established the stable FLPs by regulating the oxygen vacancies (O Vs ) of CeO 2 so as to promote the non-oxidative coupling of methane to high-value-added chemicals . As well known, CeO 2 with abundant O Vs is conducive to the formation of FLPs, and Lewis acidity and basicity in a CeO 2 matrix possess great potential for promoting the activity and hydrogenation of NO 3 – . − Therefore, the construction of the CeO 2 /BiVO 4 heterostructure would be able to impair carriers’ recombination and modulate the reaction kinetic of photocathodes.…”