Effects of Support and Synthetic Procedure for Sol-Immobilized Au Nanoparticles

Abstract

Abstract:New gold catalysts supported on CeO 2 , ZrO 2 and TiO 2 were synthesized by two different techniques: deposition-precipitation and colloidal method. The role of the surfactant (PVA, PVP, THPC) was also investigated. The catalysts were tested in the oxidation of glucose to gluconic acid, in aqueous environment and under mild conditions (60˝C and atmospheric pressure). TEM and SEM analyses have shown that the small size of gold nanoparticles is a necessary condition, but not sufficient for a good conversion. In fact, for an active sample, we have verified that the excess of surfactant must be removed because it would coat the surface of the catalyst. The surfactant, however, should not be completely eliminated, since it has the fundamental role of stabilizing the sample preventing nanoparticles from aggregation. It was evidenced that both the synthetic approach and the kind of support affect the catalysts' activity. In fact, by focusing on the three different supports, with all the preparation methods, the ceria has proved to be the best support. This is due to its ability to obtain small gold nanoparticles and to its ability to accumulate oxygen. The most appropriate synthesis methodology proved to be the colloidal method with PVA. Recyclability issue was investigated too.

Development of La Doped Ni/CeO2 for CH4/CO2 Reforming

“…An interesting compound that can be used to improve the properties of ceria support is lanthanum. It could improve the thermal stability of the support and at the same time increase the oxygen vacancies, modifying ceria redox and structural properties [56,57]. Moreover, as mentioned above, it is possible that lanthanum oxide, being basic, improves the absorption of CO 2 and its interaction with the catalyst.…”

Structural sensitivity of heterogeneous catalysts for sustainable chemical synthesis of gluconic acid from glucose

“…Their results indicated that SiO2-supported Au that featured large particles was more active during the liquid phase reaction, which indicated that the high dispersion and nature of the support were more important than the particle size. Signoretto et al [71] prepared CeO2-, TiO2-, and ZrO2-supported Au catalysts (Table 1, #22, 23, and 24, respectively) and demonstrated that the CeO2-supported Au catalyst was the most active of the three analyzed catalyst owing to its Au NPs being the smallest. In addition, CeO2 could store and deliver O2 to change the oxidation state from 3+ to 4+ [71].…”

“…Signoretto et al [71] prepared CeO2-, TiO2-, and ZrO2-supported Au catalysts (Table 1, #22, 23, and 24, respectively) and demonstrated that the CeO2-supported Au catalyst was the most active of the three analyzed catalyst owing to its Au NPs being the smallest. In addition, CeO2 could store and deliver O2 to change the oxidation state from 3+ to 4+ [71]. Au/TiO2 did not present catalytic activity owing to the metal agglomerates.…”

Towards the continuous production of Pt-based heterogeneous catalysts using microfluidic systems

“…The use of the organophosphorus salt tetrakis-(hydroxymethyl)phosphonium chloride (THPC) and its double role as stabilizing and reducing ligand, enabled an easy and versatile procedure to generate different type of noble-metal nanocrystals in conventional laboratory-scale batch reactors with 15 mL (1 mM) production scale. Afterwards, the synthesis procedure of noble metal NPs based on the double role of THPC has been successfully adopted in the production of various types of catalysts [21][22][23][24][25][26][27][28] . Although the previously reported results using THPC 20,29 were well adopted and were very promising to produce a variety of stable noble metal NPs with an exquisite size control, there are several issues that still should be improved: a) The production throughput is limited due to the long synthesis-time required (i.e., 96h); b) A reproducible, efficient and easily scalable procedure should be designed; c) NPs should be homogeneously supported in order to be applied in any heterogeneous catalytic reaction.…”