On the structure-sensitive and structure-insensitive catalytic reactions and their new characteristics, demonstrated with copper-supported catalysts

Chemistry of Aerogels and Their Applications

“…However, compared to traditional xerogels, aerogels are more recent materials for use in this field. The types of chemical reactions involved with them comprise selective oxidation such as with NiO-Al 2 O 3 and NiO-SiO 2 -Al 2 O 3 220,221 [226][227][228][229] However, active metal particles supported on oxide aerogels can also be prepared directly from a multicomponent aerogel. To obtain the metal particles, supercritical drying must be performed in a reducing environment, that is to say either in alcohol, by replacing N 2 with H 2 before heating the autoclave, or by flushing the autoclave with H 2 at approximately 200 °C.…”

“…However, compared to traditional xerogels, aerogels are more recent materials for use in this field. The types of chemical reactions involved with them comprise selective oxidation such as with NiO−Al 2 O 3 and NiO−SiO 2 −Al 2 O 3 , nitroxidation with NiO−Al 2 O 3 , selective reduction with Fe 2 O 3 −Cr 2 O 3 − Al 2 O 3 , polymerization with TiCl 4 −Al 2 O 3 , and selective hydrogenation as in the Fischer Tropsch reaction with Fe 2 O 3 −SiO 2 and Fe 2 O 3 −Al 2 O 3 . , Selective hydrogenation is mostly due to metal catalysts, and sol−gels are efficient as supports, such as with Cu−Al 2 O 3 , Ni−SiO 2 , Ni−MoO 2 , and Pd−Al 2 O 3 . − However, active metal particles supported on oxide aerogels can also be prepared directly from a multicomponent aerogel. To obtain the metal particles, supercritical drying must be performed in a reducing environment, that is to say either in alcohol, by replacing N 2 with H 2 before heating the autoclave, or by flushing the autoclave with H 2 at approximately 200 °C.…”

Aerogels

“…For the incorporation of metal components into the gel matrix, previously formed aerogels can be impregnated with solutions of the corresponding metal salts (two-step process) [118], [119]. Alternatively, metal salts can be added to the precursor solution, which results in the incorporation of the metal compounds in the gel during sol -gel processing [72], [120].…”

Particle Size Effects in the Selective Hydrogenation of Alkadienes over Supported Cu Nanoparticles

“…[5] For supported metal nanoparticles, an important parameter is their particle size. [5][6][7][8] Structure insensitive [9][10][11][12] reactions, or better reactions for which the reaction rate scales linearly with the metal specific surface area, benefit from the presence of smaller particles for obvious reasons. For structure sensitive [9][10][11][12] reactions, on the other hand, certain particle sizes give optimal catalytic performance and non-monotonic dependencies might appear.…”

“…[5][6][7][8] Structure insensitive [9][10][11][12] reactions, or better reactions for which the reaction rate scales linearly with the metal specific surface area, benefit from the presence of smaller particles for obvious reasons. For structure sensitive [9][10][11][12] reactions, on the other hand, certain particle sizes give optimal catalytic performance and non-monotonic dependencies might appear. [9][10][11][12] Hydrogenation of (poly)unsaturated hydrocarbons, a wellstudied model reaction for selective hydrogenation catalysts and very relevant in industrial applications, [13][14][15][16][17][18] is considered to be a structure insensitive reaction for most substrates and most transition metal surfaces.…”