Effect of organic capping layers over monodisperse platinum nanoparticles upon activity for ethylene hydrogenation and carbon monoxide oxidation

Abstract

The influence of oleylamine (OA), trimethyl tetradecyl ammonium bromide (TTAB), and polyvinlypyrrolidone (PVP) capping agents upon the catalytic properties of Pt/silica catalysts was evaluated. Pt nanoparticles of 1.5 nm in size were synthesized by the same procedure (ethylene glycol reduction under basic conditions) with the various capping agents added afterwards for stabilization.Before examining catalytic properties for ethylene hydrogenation and CO oxidation, the Pt NPs were deposited onto mesoporous silica (SBA-15) supports and characterized by transmission electron microscopy (TEM), H 2 chemisorption, and elemental analysis (ICP-MS). PVP and TTAB capped Pt yielded mass normalized reaction rates that decreased with increasing pretreatment temperature and was attributed to partial coverage of the Pt surface with decomposition products from the organic capping agent. Once normalized to the Pt surface area, similar intrinsic activities were obtained regardless of the pretreatment temperature, which indicated no influence on the nature of active sites. Consequently, a chemical probe technique using intrinsic activity for ethylene hydrogenation was demonstrated as an acceptable method for estimating the metallic surface areas of Pt. Amine (OA) capping exhibited a detrimental influence on the catalytic properties as severe deactivation and low activity were observed for ethylene hydrogenation and CO oxidation, respectively. These results were consistent with amine groups being strong poisons for Pt surfaces and revealed the need to consider the effects of capping agents to stabilize nanoparticles on the catalytic properties.

Catalytic properties of Pt cluster-decorated CeO2 nanostructures

“…However, for our model catalysts this technique is very challenging, due to the limited amount of metal deposited. It has been demonstrated that ethylene hydrogenation can be used as a chemical probe for estimating the number of available metallic Pt active sites in a catalyst [32]. Ethylene hydrogenation is a classic example of a structure insensitive reaction.…”

Gold Sols as Catalysts for Glycerol Oxidation: The Role of Stabilizer

“…[14,15] Studies on ethylene hydrogenation, Suzuki coupling, and CO oxidation indicated that the nature of the protective agent affects the catalytic activity of Pt, Pd, and Rh NPs. [16][17][18] Herein, we report on the aerobic oxidation of glycerol catalyzed by Au NPs with three different stabilizers, polyvinylalcohol (PVA), tetrakishydroxypropylphosphonium chloride (THPC) and citrate, with the aim to study the influence of these protective agents on the activity and stability of the Au NPs in glycerol oxidation. By using PVA and THPC, we were able to obtain small nanoparticles with comparable sizes (ca.…”

Synthesis of Pd nanocrystals enclosed by {100} facets and with sizes <10 nm for application in CO oxidation

“…The catalytic test was performed in a fixed-bed reactor (reaction conditions: flow rate 60 mL/min; 100 mg of Pd/ZnO catalyst; 2 wt% of Pd; 1.01 × 10 5 Pa pressure, 1% CO, 20% O 2 , and He balance). Before catalytic testing, all the catalysts were pretreated at 100 °C for 2 h under 10% O 2 /He (60 mL/min) [50]. Figure 4 summarizes the dependence of the CO conversion rate on the reaction temperature.…”