Ccientific Joumal from the Experimental Faculty of Cciences, at La Universidad del Zulia Volume 14 Special Nurnber
Eldad Herceg, Michael Trena
2006
Special Numbrr on Adsorption and Catalysis
unpublished
The surface chemistry of carbon-nitrogen coupling is of fundamental irnportance to the industrial scale catalytic synthesis of HCN from CH, and NH, over Pt gauze catalysts. In order to elucidate the details of the synthesis, we investigated the mechanism of CN bond formation on Pt(l11) with reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD). The relevant surface intermediates were generated through the thermal decomposition of CH31 or C,H, and the
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... ctron induced dissociation or oxydehydrogenation of NH,. The formation of surface CN is detected through HCN desorption a t 500 K in theTPD experiments. The appearance of the vibrational features characteristic of the arninocarbyne (CNH,) species upon hydrogenation of surface CN at 300 K in the RAIR spectra has been used to establish sh the CN bond formation temperature. The RAIRS results indicate that HCN desorption a t 500 K is kinetically limited by the formation of the CN bond at this temperature from surface C and N atoms. The formation of CN is suppressed in the presence of high coverages of surface carbon, in agreement with previous model reactor kinetic studies. In contrast, the coverage and overlayer structure of surface nitrogen has a negligible influence on the coupling reaction. Our results indicate that the high temperatures used in the industrial synthesis of HCN are needed pnmarily to activate methane and arnmonia dissociative adsorption on the Pt catalyst surface. Rey words: Pt(l1 l), infrared absorption spectroscopy, temperature programmed desorption, aminocarbyne, hydrogen cyanide synthesis. Acoplamiento carbon-nitrógeno sobre Pt(ll1) y su importancia en la síntesis catalítica de HCN Resumen La química superficial del acoplamiento carbono-nitrógeno es de fundamental importan-cia a escala industrial en la síntesis de HCN a partir de CH, y NH, sobre catalizadores de malla de Pt. Con la finalidad de dilucidar los detalles de la síntesis, nosotros investigamos la forma-ción del enlace CN sobre Pt(1 l l) con espectroscopía de reflexión absorción infrarroja (RAiRS) y desorción a temperatura programada (TPD). Los intermediarios superficiales relevantes fueron generados a través de la descomposición térmica de CH31 o C,H, y la disociación inducida del electrón o oxideshidrogenación de NH,. La formación de CN superficial es detectada a través de * Autor para la correspondencia.
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