The effect of the addition of sodium compounds in the liquid-phase hydrodechlorination of chlorobenzene over palladium catalysts

The hydrodechlorination of chlorobenzene over supported palladium catalysts has been studied. The palladium catalysts: deactivate as the reaction proc eeds due to the HCl formed as by-product. The effect of the addition of sod ium compounds has been analysed for the neutralisation of HCl. When NaOH wa s added to the reaction mixture, no beneficial effect was observed due to t he detrimental effect of the alkaline medium on the textural and metallic p roperties of the catalysts. Doping the support with NaOH prior to impregnat ion with the metal precursor leads (after calcination and reduction) to cat alysts with better activity and tolerance to deactivation, especially those obtained when using PdCl2 as the metal precursor. Low metal dispersion and the capture of chloride by forming NaCl are the: main factors contributing to the: improved catalytic properties. Finally, doping the catalysts with NaOH or NaNO3, after reduction of the metal precursor leads to a moderate i ncrease in initial activity and final conversion, although NaOH impregnatio n also gave rise to support corrosion and metal dispersion modification. (C ) 2001 Elsevier Science B.V, All rights reserved.