A theoretical comparison of Lewis acid vs bronsted acid catalysis for n-hexane --> propane + propene.

نویسندگان

  • Qingbin Li
  • Ken C Hunter
  • Allan L L East
چکیده

Cracking of an all-trans n-alkane, via idealized Lewis acid and Bronsted acid catalysis, was examined using density functional theory. Optimized geometries and transitions states were determined for catalyst-reactant complexes, using AlCl3 and HCl.AlCl3 as the Lewis and Bronsted acids. For the Lewis acid cycle, hydride-transfer steps are seen to have large barriers in both forward and reverse directions, and an unstable physisorbed carbenium ion (lying 20 kcal mol(-1) above the chemisorbed intermediate) is the launching point for the beta-scission that leads to products. For the Bronsted acid cycle, proton-transfer steps have smaller barriers in both forward and reverse directions, and a semistable physisorbed alkanium ion is the launching point for the alkanium alpha-scission that leads to products. In the idealized Lewis cycle, formation of HCl units (and hence Bronsted acids) was found to be a common side reaction. A recent ionic-liquid catalysis study is mentioned as motivation, although our study is not a computational modeling study; we are more interested in the fundamental differences between Brosnted and Lewis mechanisms rather than merely mimicking a particular system. However, results of exploratory optimizations of various intermediates with Al2Cl7- as the catalyst are presented to provide the first step for future modeling studies on the ionic liquid system.

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Application of silica vanadic acid as a dual Lewis and Bronsted acid catalytic ability in Dakin West reaction

Silica Vanadic Acid, SVA, (oxo-vanadium has been supported on silica) as a dual Lewis and Bronsted acid ability was prepared and efficiently catalyzed one-pot multi-component condensation of enolizable ketones or alkyl acetoacetates with aromatic aldehydes, acetonitrile and acetyl chloride. The described reaction was produced β-acetamido ketone or ester derivatives in high to excellent yields i...

متن کامل

Application of silica vanadic acid as a dual Lewis and Bronsted acid catalytic ability in Dakin West reaction

Silica Vanadic Acid, SVA, (oxo-vanadium has been supported on silica) as a dual Lewis and Bronsted acid ability was prepared and efficiently catalyzed one-pot multi-component condensation of enolizable ketones or alkyl acetoacetates with aromatic aldehydes, acetonitrile and acetyl chloride. The described reaction was produced β-acetamido ketone or ester derivatives in high to excellent yields i...

متن کامل

Solvent-free synthesis and characterization of antibacterial azo dyes in the presence of Bronsted-acid ionic liquid as a green catalyst

A convenient and efficient direct protocol for the preparation of antibacterial azo dyes by the reaction of 2-naphthol with aromatic amines in the presence of catalytic amount of N-methyl-2-pyrrolidonium hydrogen sulfate ([H-NMP]HSO4) was carried out under solvent free conditions. This method has some advantages such as: easy work-up and easy separation of catalyst from the reaction mixture. Th...

متن کامل

Operating condition effect on achieving higher propene yield in propane oxidative dehydrogenation process

Supported vanadia catalyst was successfully synthesized using wet impregnation of gamma-Alumina to study Propane Oxidative Dehydrogenation (POD). The prepared catalysts were characterized with XRD, BET, and TPR tests. In a broad temperature range (340 to 630°C), effects of vanadia loading (2.7, 5.4, and 9 wt%) and propane to oxygen ratio (3/1 to 1/3) were investigated on propane conversion as w...

متن کامل

Solvent-free synthesis and characterization of antibacterial azo dyes in the presence of Bronsted-acid ionic liquid as a green catalyst

A convenient and efficient direct protocol for the preparation of antibacterial azo dyes by the reaction of 2-naphthol with aromatic amines in the presence of catalytic amount of N-methyl-2-pyrrolidonium hydrogen sulfate ([H-NMP]HSO4) was carried out under solvent free conditions. This method has some advantages such as: easy work-up and easy separation of catalyst from the reaction mixture. Th...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:
  • The journal of physical chemistry. A

دوره 109 28  شماره 

صفحات  -

تاریخ انتشار 2005