Hydrogenolysis of alkanes and olefin polymerization on the silica-supported zirconium hydrides: A comparative DFT study

Abstract

The model reactions of ethylene polymerization and hydrogenolysis of linear alkanes (propane, n-butane, and n-pentane) on the silica-supported zirconium hydrides (BSiAO) 3 Zr IV H, (BSiAO) 2 Zr IV H 2 , and (BSiAO) 2 Zr III H were studied using the DFT approach. Catalytic processes under study were shown to occur involving different surface hydrides. The ethylene polymerization was found to proceed at comparable rates on the zirconium monohydrides, (BSiAO) 3 ZrH, and dihydrides, (BSiAO) 2 ZrH 2 . Cleavage of linear alkanes on the monohydrides (BSiAO) 3 ZrH is thermodynamically unfavorable; however, the dihydrides (BSiAO) 2 ZrH 2 can act as catalysts of the process under mild conditions. Hydrides of the trivalent zirconium, (BSiAO) 2 Zr III H, can also contribute to the hydrogenolysis reaction. A feature of all the systems studied is low regioselectivity of the corresponding processes.

H/D Exchange on Silica-Grafted Tantalum(V) Imido Amido [(≡SiO)2Ta(V)(NH)(NH2)] Synthesized from Either Ammonia or Dinitrogen: IR and DFT Evidence for Heterolytic Splitting of D2

“…The tantalum atom is covalently bonded to two vicinal oxygen surface atoms leading to a non-constrained 6-membered ring [{(l-O)[(HO) 2 SiO] 2 }Ta(NH)(NH 2 )], 2 q, whose notation will be simplified to [(-SiO) 2 Ta(NH)(NH 2 )]. This model is very similar or equal to those used in previous studies for modeling silica-supported transition metal hydrides [63][64][65][66][67][68]. The reliability of the representation of 2T (Si 2 O 7 H 4 )Ta has been verified by comparing the structures and energetics of all minima obtained with the cluster model with those obtained with the periodic calculations, using (C (100) ) as model for silica.…”

Synergy between Two Metal Catalysts: A Highly Active Silica-Supported Bimetallic W/Zr Catalyst for Metathesis of n-Decane

“…In this context, we decided to use Zr­(Np) 4 because silica-supported [Si–O–Zr­(Np) 3 ] has already been reported by us and was fully characterized at the molecular level using solid-state NMR, IR, elemental analysis, and gas quantification methods. The corresponding [(Si–O−) 4– x Zr­(H) x ] is known to be very active in the hydrogenolysis and C–H bond activation reaction. , …”

“…The corresponding [(≡Si-O-) 4-x Zr(H) x ] is known to be very active in hydrogenolysis and C-H bond activation reaction. 23,24 Herein, we disclose the synthesis and molecular level characterization of a well-defined, silica supported, bimetallic precatalyst [≡Si-O-W(CH 3 ) 5 ≡Si-O-Zr(Np) 3 ](4) (Scheme 1) which upon thermal treatment at 100 o C transforms to a mixture of methylidyne species (5) (Scheme 2). The precatalyst 4 was converted into its corresponding hydrides, by the treatment with hydrogen at room temperature 6 and at high temperature, 7 respectively (Scheme 3).…”

Surface Organometallic and Coordination Chemistry toward Single-Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities

“…DFT calculations on cluster or extended models also agree with the mechanism in Scheme 58. 456,588,589 These studies suggest that C−H bond activation corresponds occurs via a σbond metathesis, 487 which is easier on dihydride than monohydride surface species (Scheme 58c). 458 Hydrogenolysis of alkanes is also observed in the presence of H 2 with Zr hydrides supported on alumina 459 or aminemodified SBA15 (Scheme 57c,d).…”