8.4.2 adsorption on solid surface (3)Kind of adsorption Chemisorption b p involves the formation of chemical bonds between adsorbed molecule and solid surface y physisorption and often involving the breaking of preexisting bonds in the adsorbed molecule. In some cases D the chemisorption step requires an activation chemisorption energy hydroxy-terminated surface 2d:: hysi-sorption 8=HS-(CH)b-OH involves forces similar to the intermolecular forces/ weak interaction that lead to condensation of vapors to liquid
Chemisorption involves the formation of chemical bonds between adsorbed molecule and solid surface, and often involving the breaking of preexisting bonds in the adsorbed molecule. In some cases the chemisorption step requires an activation energy. physi-sorption involves forces similar to the intermolecular forces / weak interaction that lead to condensation of vapors to liquid. b.p. (3) Kind of adsorption 8.4.2 adsorption on solid surface
8.4.2 adsorption on solid surface (3)Kind of adsorption The potential curve of adsorption 2Ni+ 2H Transition from physisorption to chemisorption 2Ni+h H-H By following the transition from physical H absorption to chemical adsorption, catalysts Transition state can activate reactant molecules at relatively 8:: mild conditions. This is the basic principal for heterogeneous catalysis Physical adsorption Chemical adsorption
Transition from physisorption to chemisorption The potential curve of adsorption By following the transition from physical absorption to chemical adsorption, catalysts can activate reactant molecules at relatively mild conditions. This is the basic principal for heterogeneous catalysis. Physical adsorption Transition state Chemical adsorption 2Ni + H2 2Ni + 2H −Ni−Ni− H H −Ni−Ni− H−H (3) Kind of adsorption 8.4.2 adsorption on solid surface
8.4.2 adsorption on solid surface (3)Kind of adsorption Comparison between chemical and physical adsorption sorption physisorption chemisorption Interaction Thermal effect temperature Adsorbed layer reversibility selectivity
sorption physisorption chemisorption interaction Thermal effect temperature Adsorbed layer reversibility selectivity Comparison between chemical and physical adsorption (3) Kind of adsorption 8.4.2 adsorption on solid surface
8.4.2 adsorption on solid surface (4)Thermodynamic aspects of adsorption △G=△H-TAS Conditions for chemisorption Adsorption is spontaneous, AG<O 2W+n2=2 W-Nad Entropy decreases during AS<0 adsorption AadsHm=D(N2)-2X (W-N)<0 Therefore △H<0 adsorption is a exothermic process
G = H −TS Adsorption is spontaneous, G 0 Entropy decreases during adsorption S 0 H 0 adsorption is a exothermic process Therefore: (4) Thermodynamic aspects of adsorption Conditions for chemisorption 2W + N2 = 2 W-Nad adsHm = D(N2 ) – 2X (W-N) < 0 N2 W-N 2 D X 8.4.2 adsorption on solid surface
8.4.3 expressions of adsorption
8.4.3 expressions of adsorption