Formation of carbon-carbon coupling compounds from difluorodichloromethane

The objective of the work presented in this thesis was to apply the tools of reaction kinetics and catalysis to convert the ozone depleting chlorofluorocarbons (CFCs) into environmentally benign and industrially useful compounds and at the same time to understand the fundamentals of the halocarbon conversion reactions to synthesize catalysts that can increase the selectivity toward a desired reaction pathway in the presence of competing pathways.; The ozone depleting nature of CFCs has resulted in several investigations over past 20 years, to convert the existing feedstock of CFCs into benign compounds and to find alternatives for CFCs. A novel route to convert C ₁ CFCs such as difluorodichloromethane (CF₂Cl₂) into industrially significant commodities such as tetrafluoroethylene (C ₂F₄) and ethylene (C₂H₄), through C-C coupling reactions on the catalyst surface, was investigated in this thesis. As a first step to understand the chemistry that governs the formation of C₂₊ products, the catalytic behavior of the known hydrodechlorination catalysts, group VIII noble metals Ru, Rh, Pd, Os, Ir and Pt supported on activated carbon (BPLF 3), was investigated at 523 K and CF₂Cl ₂:H₂ ratios of 0.2 and 1 (Chapter 3). This investigation suggested that the carbene (:CH₂) and fluorocarbene (:CF₂ ) surface species could interact to produce C₂F₄, CF₂CH₂ and hydrocarbons (C₂ and C₃). The Pd/C catalyst showed 75% selectivity toward hydrocarbon coupling products. The fluorinated coupling products were produced with <5% selectivity on monometallic catalysts Ru, Rh, Os and Ir/C.; The observation that the properties of the metal strongly influence the selectivity pattern during the reaction of CF₂Cl₂ and H₂, led to investigation of group IB (Cu, Ag) and group VIII (Fe, Co) metals as potential catalysts for producing C-C coupling products. However, these metals were found to be inactive under the reaction condition, as they cannot dissociate H₂ readily to keep the catalyst surface active in the poisoning reaction atmosphere containing Cl and F. The work described in Chapter 4 and Chapter 5 showed that the potential of group IB and group VIII metals to couple the reaction intermediates could be utilized if the catalyst surface is modified by adding a metal such as Pt or Pd that can act as a source of dissociated H atoms. A dual site mechanism was suggested where Pt or Pd acted as a source of H atoms and coupling of reaction intermediates took place on group IB or group VIII metals.; The Pt-Cu bimetallic catalyst supported on activated carbon BPLF 3 was investigated further to understand the role of each metal and the nature of active site (Chapter 7). The selectivity toward hydrocarbon coupling products, during initial 3–5 min, increased as the Cu concentration in the bimetallic catalyst increased. This result is consistent with the hypothesis that formation of coupling products takes place on Cu sites. The bimetallic catalysts containing were also found to produce coupling compounds starting from C₁ halocarbons such as CH₂Cl₂.