T. N. Bell

Catalytic conversion of CCl2F2 on Pt/γ-Al2O3 catalyst

The reaction of CCl2F2 (CFC 12) with hydrogen has been studied on a Pt/γ-Al2O3 catalyst containing 0.5, 2 and 5 wt % of Pt at a temperature of 300°C and on 2% Pt at other temperatures. The product selectivity (distribution), and the extent of conversion, was shown to be highly dependent both on the metal coverage and on the temperature.

31P and119Sn high resolution solid state CP/MAS NMR study of Al2O3-SnO2 systems

A series of Al2O3-SnO2 catalysts with the mole ratio of Al2O3 to SnO2 equal to 1:1, 1 ∶ 0.5, 1 ∶ 0.1, 1 ∶ 0.05 and 1 ∶ 0.01 were characterized by31P NMR of adsorbed trimethyl phosphine (TMP) and119Sn MAS NMR spectroscopy. It was found from31P NMR that no Brønsted acid sites exist in these samples. Pure SnO2 shows two different types of Lewis acid sites; in the mixed oxide samples a Lewis peak characteristic of pure Al2O3 is always seen, together with either one or two other Lewis peaks, depending on the Sn concentration.119Sn CP/MAS NMR spectra of the highest Sn-content sample show one narrow line at −603 ppm superimposed on a very broad line, indicating a strong interaction between Al and Sn oxides.

Studies of physicochemical and surface properties of alumina modified with rare earth oxides. II: Porous structure

Results are presented of investigations of the porous structure of the Al2O3-La2O3 systems containing up to 10 wt% of the La modifying oxide prepared by the coprecipitation method. Pore size distribution was determined on the basis of low temperature nitrogen adsorption measurements and mercury intrusion porosimetry. The changes in pore size distribution of different forms of Al2O3-La2O3 are discussed in relation to the concentration of the lanthanum oxide.

Effect of hydrogen treatment on the porous structure of Al2O3-SnO2 system

The results of an investigation of the porous structure of the Al2O3-SnO2 system and its properties after hydrogen treatment are presented. Pore size distribution was determined on the basis of low temperature nitrogen adsorption measurements. Reduction of the system by H2 leads to a decrease of the parameters defining porous structure. We conclude that this is due to the reduction of Sn(IV) species to oxidation state II.

31-P NMR study study of acidic sites on Al2O3 and Al2O3-SnO2 after reaction with CCl2F2/H2

The surface acidic properties of two series of samples,γ-Al2O3 andγ-Al2O3-SnO2 after reaction with CCl2F2/H2 (CFC12/H2), have been investigated by solid state high resolution CP/MAS 31-PNMR, using trimethylphosphine (TMP) as a probe molecule. It was found after reaction, that Brønsted acid sites were formed on theγ-Al2O3 surface. The longer the reaction time, the more rigidly TMP bonded to the acid sites. For theγ-Al2O3-SnO2 system, Brønsted acid sites were also found on both the Al2O3 and SnO2 surfaces after reaction of theγ-Al2O3-SnO2 system with CFC12/H2. The signal intensity relevant to these sites, indicates that the SnO2 component is attached to, and therefore covers Brønsted sites ofγ-Al2O3. Two types of Lewis acid site initially present on SnO2 were not observed after reaction with CFC12/H2.

Catalytic Hydrodehalogenation of CFC’s (Freons)

The photolysis of fully halogenated chlorofluorocarbons (CFC’s) in the stratosphere, and their resultant role in ozone depletion is of great global concern1. In addition to the role played by CFC’s in the destruction of ozone, they also contribute to the “green-house effect” and hence to climatic changes2. The replacement of halogen by hydrogen makes the halo-carbon susceptible to destructive free radical attack in the troposphere and considerably reduces the depletion of ozone3–6. The following reaction may serve as a pertinent example: n n

31-P NMR study study of acidic sites on Al 2 O 3 and Al 2 O 3 -

{text{CC}}{{text{l}}_2}{{text{F}}_2}xrightarrow[{{text{catalyst}}}]{{{{text{H}}_2}}}{text{C}}{{text{H}}_{text{2}}}{{text{F}}_2} + {text{HCl}}({text{HF}})