Polymer-Induced Selectivity Enhancement in the Hydrogenation of 2-Hexyne Catalyzed by Poly(vinylpyrrolidone)-Stabilized Platinum Colloids in an Amorphous Mixed Metal Oxide Support

Abstract

Poly(vinylpyrrolidone) (PVP)-stabilized Pt clusters (1.4 nm average particle size) were embedded in an amorphous microporous titania-silica mixed oxide (AMM-Me Si30Ti) by means of a modified sol-gel procedure. The Pt particles were shown by transmission electron microscopy to retain their approximate original average diameter. The catalytic activity of the Pt-colloid-containing titania-silica mixed oxide catalysts was tested with the hydrogenation of 2-hexyne at 1 bar in decane or 1-propanol in a batch reactor. Selectivities to cis/trans-2-hexene were higher than those for PVP-stabilized colloids dispersed in the liquid phase. In colloidal dispersions of the PVP-stabilized catalyst in propanol, an initial 2-hexene selectivity of 80% at a conversion of <10% fell to ca. 45% at 100% conversion. With the AMM-supported catalyst, a 2-hexene selectivity of >94% was observed at hexyne conversions up to 50%, and at complete conversion a selectivity to 2-hexenes of 88% was achieved (cis-2-hexene selectivity of 91%). Thermal treatment of the platinumcontaining AMM-Me Si30Ti in an oxygen atmosphere leads to the removal of the protective PVP shell surrounding the colloids inside the sol-gel material, as detected by 13 C-MAS NMR spectroscopy, resulting in an increase in both surface area and Pt particle size. The resulting catalysts showed lower selectivity for 2-hexene. A control experiment showed that the presence of PVP was responsible for the high selectivities to cis/trans-2-hexene exhibited by the AMM-supported colloidal Pt catalysts.

Enhanced Photocatalytic Activity of Pure Anatase Tio2 and Pt-Tio2 Nanoparticles Synthesized by Green Microwave Assisted Route

“…Such compounds passivate the particle surface, so that nanoparticles lose their active sites and therefore affect the photocatalytic process 19 . In order to remove these substances, plasma cleaning 20 , calcinations 21 , super-hydride reaction 17 , heat 22 and high-temperature hydrogen treatments 23 have been reported in literature. These techniques, however, either require expensive special equipment or can compromise the morphological integrity of the nanoparticles due to harsh treatment conditions.…”

Characterization of Colloidal Platinum Nanoparticles by MALDI-TOF Mass Spectrometry

“…[7][8][9][10][11][12][13] In one instance, enhanced selectivity for the hydrogenation of 2-hexyne has been suggested to be the result of surface modification by the PVP capping agent. 12 In another case, the quantity of the PVP capping agent present has been observed to influence catalytic activity.…”

“…[7][8][9][10][11][12][13] In one instance, enhanced selectivity for the hydrogenation of 2-hexyne has been suggested to be the result of surface modification by the PVP capping agent. 12 In another case, the quantity of the PVP capping agent present has been observed to influence catalytic activity. 13 Taken together, these findings suggest that for catalytic applications using these colloidal nanoparticles in solution, knowledge of both the interaction of the capping agent with the nanoparticle and the particle size are crucial for optimizing the activity and selectivity of catalytic reactions.…”

Organometallic Nanoparticles of Metals or Metal Oxides

“…PVP coated particles of this type were embedded into an amorphous microporous titania-silica mixed oxide by means of a modified sol-gel procedure. The resulting material was found more selective than both the PVP coated nanoparticles in solution and platinum particles on the mixed oxide without polymer for the hydrogenation of 2-hexyne into cis-2-hexene [31].…”

“…These experimental procedures are not specific of the phosphine ligands and may be employed using more classical ligands for nanoparticles such as octanethiol [31]. In this case, a very stable colloid is formed which may be isolated from the reaction medium and re-dissolved for reactivity or spectroscopic studies.…”