Propylene epoxidation kinetics

A factorial design of kinetic experiments utilizing Au/TS-1 was the first study of propylene epoxidation kinetics in the absence of catalyst deactivation [55]. The adoption of a factorial design allowed for the examination of the largest statistically significant number of reaction conditions centered around the standard reaction mixture of 10/10/10/70 vol% Fl2/02/propylene/diluent while avoiding flammable conditions. The experimental results [55] from the evaluation of three Au/TS-1 catalysts showed that PO production could be approximated using the power rate law expression rpo = k [Fl2] [O2] [CsHe]... 

In this article, a dynamic reaction kinetics for propylene epoxidation on Au/Ti02 is presented. Au/Ti02 catalyst is prepared and kinetics experiments are carried out in a tube reactor. Kinetic parameters are determined by fitting the experiments under different temperatures, and the reliability of the proposed kinetics is verified by experiments with different catalyst loading. 

Unfortunately, the absence of kinetic data in Ref. [70] does not allow more comprehensive consideration of the interaction between synchronously proceeding H202 dissociation and propylene epoxidation processes. 

Effective kinetic and thermodynamic parameters of propylene epoxidation with hydrogen peroxide on biomimic (perFTPhPFe(III)0H/Al203)... 

L. Siimegi, I. P. Hajdu, I. Nemes, A. Gedra, On the mechanism of propylene epoxidation catalyzed by molybdenum naphthenate. React. Kinet. Catal. Lett. 12 (1979) 57. 

J. Q. Lu, X. Zhang, J. J. Bravo-Suarez, S. Tsubota, J. Gaudet, S. T. Oyama, Kinetics of propylene epoxidation using H2 and O2 over a gold/mesoporous titanosilicate catalyst, Catal. Today 123 (2007) 189. 

Key Words Direct propylene epoxidation. Propylene oxide, Gold, Titanium, Propene, Au/Ti catalysts. Catalysis by gold. Titanium silicalite, TS-1, Gold/TS-1, Hydrogen peroxide, Kinetics, Design of experiments, Deposition-precipitation, Ammonium nitrate, Selective oxidation, Alkene epoxidation, Density functional theory, DFT calculations, QM/MM calculations. 2008 Elsevier B.v. 

Even well-made TS-1 contains a small fraction of Si-vacancy defects [73,74]. Consistent with FTIR results on H2O2/TS-I [75], previous DPT calculations on nondefect (tetrapodal) and metal-vacancy defect (tripodal) Ti sites in TS-1 suggested that H2O2 attack on Ti-defect sites leads to Ti-OOH species (and water), while H2O2 attack on Ti-nondefect sites is kinetically and thermodynamically less favorable [76]. Moreover, Ti-OOH species can catalyze propylene epoxidation to PO [76-78]. Recent QM/MM calculations on adsorption of Aui 5 clusters inside the TS-1 pores suggest that the Ti-defect site is also the most favorable binding site for small Au clusters [66]. Therefore, defects in TS-1 are likely to stabilize adsorbed Au clusters and prevent sintering. 

FIGURE 14.9 Test of pseudo-first-order kinetic model for propylene epoxidation with ethylbenzene hydroperoxide (EBHP) over Ti/MCM-41. 

In the present study, our interest is focused on a membrane reactor in which the membrane can be employed as a large pore catalyst for the convection flow of reactants. Propylene epoxidation to produce propylene oxide (PO) is taken as a model reaction of parallel-consecutive reactions by using a Re-Ag immobilized in the pores of a micro-porous-glass membrane (MPG). The objectives of this paper are to clarify (1) the reaction kinetics in partial and total oxidation differing from the packed bed reactors,... 

Bravo-Suarez, J., Lu, J., DaUos, C., et al. (2007). Kinetic Study of Propylene Epoxidation with Ho and Oo over a Gold/Mesoporous Titanosilicate Catalyst, J. Phys. Chem. C, 111, pp. 17427-17436. 

Currently there are four major lines of approach towards gas-phase epoxidation of propylene (1) mechanistic studies of Au/Ti02 catalysts through kinetics, spectroscopic identification of adsorbed species and... 

Carbon dioxide is one of the most abundant carbon resources on earth. It reacts with an epoxide to give either a cyclic carbonate or a polycarbonate depending on the substrates and reaction conditions. Kinetic resolution of racemic propylene oxide is reported in the formation of both cyclic carbonate and polycarbonate. The fe ei value defined as ln[l-(conversion)(l+%ee)]/ln[l-(conversion)(l% ee)] reached 6.4 or 5.6 by using a Co(OTs)-salen complex with tetrabutylammonium chloride under neat propylene oxide or using a combination of a Co-salen complex and a chiral DMAP derivative in dichloromethane, respectively. 

Based on the landmark studies of Jacobsen and coworkers, who employed chiral (salen)CoX complexes for the asymmetric ring opening and kinetic resolution of aliphatic epoxides [18-20], Lu and coworkers synthesized highly isotactic copolymer from rac-propylene oxide and carbon dioxide (Scheme 5) [21]. 

Pawela Crew and Madix [144] have investigated desorption of propylene and propane from Ag(llO) with the emphasis put on the anomalous effects of weak chemisorption on desorption kinetics of alkenes. Molecular conformation of styrene on Ag(lOO) related to the catalytic epoxidation of terminal alkenes has been studied by Williams etal. [145]. IR studies of the adsorption structures of 1,3-butadiene at Ag(lll) and Au(lll) surfaces have been published by Osaka et al. [146]. 

Carbocation-oxonium ion equilibria are obvious complicating factors in studies of the kinetics of initiation of polymerisation and useful thermodynamic data for such equilibria involving Ph3C+ and a variety of linear and cyclic ethers have been reported by Slomkowski and Penczek (132). A dramatic increase in rates of initiation of polymerisation of THF induced by Ph3C+ salts is observed on addition of small amounts of epoxides such as propylene oxide (113a,b), which compete favourably with THF in the primary carbocation-oxonium ion equilibria and simplify the initiation reaction ... 

Describing the reaction in kinetic terms, let us apply to the fact that the intermediate perFTPhPFe3+00H/Al203 formation stage (7.7) is fast, the epoxide formation stage (7.8) is slow and, consequently, limiting. For kinetic simulation of propylene oxidation to epoxide, this gives an opportunity to apply the Michaelis-Menten equation in Linuver-Berk coordinates ... 

A so far still unsolved problem is the direct enantioselective epoxidation of simple terminal olefins. For example the epoxidation of propylene that was achieved with a 41% ee almost twenty years ago by Strukul and his coworkers using Pt/diphosphine complexes is still unsurpassed. Unfortunately such low ee s are of no practical interest. The problem was circumvented by Jacobsen using hydrolytic kinetic resolution of racemic epoxides (Equation 26) and is practised on a multi 100 kg scale at Chirex. The strategy used is to stereose-lectively open the oxirane ring of a racemic chiral epoxide leaving the other enantiomer intact. Reactions are carried out to a 50% maximum conversion. The catalyst belongs to the metal-salen class described above and can be recycled. The products are separated by fractional distillation. 

A number of theoretical studies have appeared on the mechanism of the oxirane-forming reaction of olefins and 0( P). A kinetic investigation of the reaction of oxirane and the 0( P) atom has shown that H-abstraction occurs rather than insertion to form a dioxetane intermediate, The thermal and photochemical epoxidation of propylene in the presence of sulfur dioxide and acetonitrile have been reported. ... 

Kinetic and isotopic labeling studies by Long and Pritchard on the hydrolyses of ethylene oxide, propylene oxide and isobutylene oxide to their corresponding glycols provide additional insight on the hydrolysis mechanisms of simple aliphatic epoxides.23 In each case, three kinetically distinct mechanisms for their reactions in water solutions were observed acid-catalyzed hydrolysis, pH-independent hydrolysis and hydroxide-catalyzed hydrolysis. Thus, the rate law for hydrolyses of these simple... 

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