Effect of Supports on the Gold Catalyst Activity for Catalytic Combustion of CO and HCHO

A Review of Noble Metal Catalysts for Catalytic Removal of VOCs

Volatile organic compounds (VOCs) are important precursors for the formation of secondary pollutants, such as fine particulate matter (PM) and ozone (O3), which will lead to severe atmospheric environmental problems to restrict the sustainable development of the social economy. Catalytic oxidation is a safe, eco-friendly, and simple method for eliminating VOCs, which can be converted into CO2 and H2O without the generation of other harmful substances. The fabrication and development of catalysts are very crucial to enhance the catalytic oxidation efficiency of the removal of VOCs. The noble metal catalyst is one of the commonly used catalysts for the catalytic oxidation of VOCs because of the high reaction activity, good stability, poisoning-resistant ability, and easy regeneration. In this review, the research progress of noble metal (Pt, Pd, Au, Ag, and Ir) catalysts for the removal of VOCs in recent years was summarized with the discussion of the influence factors in the preparation process on the catalytic performance. The reaction mechanisms of the removal of VOCs over the corresponding noble metal catalysts were also briefly discussed.

Gold Nanoparticle-Functionalized Diatom Biosilica as Label-Free Biosensor for Biomolecule Detection

Diatom biosilica (DBs) is the cell wall of natural diatom called frustule, which is made of porous hydrogenated amorphous silica possessing periodic micro- to nanoscale features. In this study, a simple, sensitive, and label-free photoluminescence (PL) immune-detection platform based on functionalized diatom frustules was developed. Gold nanoparticles (AuNPs) deposited on poly-dopamine-coated diatom frustules via in situ deposition which considerably decreased the intrinsic blue PL intensity of diatom biosilica. Then, goat anti-rabbit immunoglobulin G (IgG) was added to functionalize diatom biosilica-poly-dopamine-AuNPs (DBs-PDA-AuNPs). PL studies revealed that the specific binding with antigen rabbit IgG increased the peak intensity of PL in comparison with the non-complimentary antigen (human IgG). The enhancement in PL intensity of DBs-PDA had a linear correlation with antigen (rabbit IgG) concentration, whose limit of detection (LOD) reached 8 × 10^-6 mg/ml. Furthermore, PL detection based on DBs-PDA-AuNPs showed a high detection sensitivity with the LOD as low as 8 × 10^-9 mg/ml and spread over almost eight orders of magnitude, making it suitable for the sensitive quantitative analysis of immune complex compared with traditional fluorescence immunoassay. Hence, the study proves that the AuNP-functionalized diatom frustules can serve as an effective biosensor platform for label-free PL-based immunoassay.

Novel Materials for Combined Nitrogen Dioxide and Formaldehyde Pollution Control under Ambient Conditions

Formaldehyde (HCHO) and nitrogen dioxide (NO2) often co-exist in urban environments at levels that are hazardous to health. There is a demand for a solution to the problem of their combined removal. In this paper, we investigate catalysts, adsorbents and composites for their removal efficiency (RE) toward HCHO and NO2, in the context of creating a pollution control device (PCD). Proton-transfer-reaction mass spectrometry and cavity ring-down spectrometry are used to measure HCHO, and chemiluminescence and absorbance-based monitors for NO2. Commercially available and lab-synthesized materials are tested under relevant conditions. None of the commercial adsorbents are effective for HCHO removal, whereas two metal oxide-based catalysts are highly effective, with REs of 81 ± 4% and 82 ± 1%, an improvement on previous materials tested under similar conditions. The best performing material for combined removal is a novel composite consisting of a noble metal catalyst supported on a metal oxide, combined with a treated active carbon adsorbent. The composite is theorized to work synergistically to physisorb and oxidize HCHO and chemisorb NO2. It has an HCHO RE of 72 ± 2% and an NO2 RE of 96 ± 2%. This material has potential as the active component in PCDs used to reduce personal pollution exposure.

Platinum-Supported Zirconia Nanotube Arrays Supported on Graphene Aerogels Modified with Metal-Organic Frameworks: Adsorption and Oxidation of Formaldehyde at Room Temperature

Precious-metal catalysts (e.g., Au, Rh, Ag, Ru, Pt, and Pd) supported on transition-metal oxides (e.g., Al₂ O₃ , Fe₂ O₃ , CeO₂ , ZrO₂ , Co₃ O₄ , MnO₂ , TiO₂ , and NiO) can effectively oxidize volatile organic compounds. In this study, porous platinum-supported zirconia materials have been prepared by a "surface-casting" method. The synthesized catalysts present an ordered nanotube structure and exhibited excellent performance toward the catalytic oxidation of formaldehyde. A facile method, utilizing a boiling water bath, was used to fabricate graphene aerogel (GA), and the macroscopic 3D Pt/ZrO₂ -GA was modified by introducing an adjustable MOF coating by a surface step-by-step method. The unblocked mesoporous structure of the graphene aerogel facilitates the ingress and egress of reactants and product molecules. The selected 7 wt.% Pt/ZrO₂ -GA-MOF-5 composite demonstrated excellent performance for HCHO adsorption. Additionally, this catalyst achieved around 90 % conversion when subjected to a reaction temperature of 70 °C (T_90 % =70 °C). The Pt/ZrO₂ -GA-MOF-5 composite induces a catalytic cycle, increasing the conversion by simultaneously adsorbing and oxidizing HCHO. This work provides a simple approach to increasing reactant concentration on the catalyst to increase the rate of reaction.

Au/Co promoted CeO2 catalysts for formaldehyde total oxidation at ambient temperature: role of oxygen vacancies

Cobalt enables formation of additional oxygen vacancies in Au/Co–CeO₂ and significantly boosts the ambient oxidation of formaldehyde.

Toward effective design and adoption of catalyst-based filter for indoor hazards: Formaldehyde abatement under realistic conditions

Catalytic oxidation at ambient temperature has drawn wide attention as a new promising method of air cleaning, converting hazardous materials into non-hazardous ones. However, limited information is available regarding catalytic filter performance/characteristics under real operating conditions, especially on service efficiency and byproducts. Also, no practical scale-up method/evidence for filter performance evaluation is currently available to scale-up laboratory results to real application conditions. These limitations and knowledge gaps prevent building owners/designers from adopting this new promising technique in their commercial/industrial applications. The present study conducted experiments from small-scale to full-scale chamber tests which challenged a developed catalytic filter under realistic conditions. Formaldehyde was selected for approach demonstration due to its indoor ubiquitousness and criticality for human health even at low-levels. Results showed that the competition level for reaction sites in filter media had a crucial role in the performance for formaldehyde abatement, a high initial (77%; under no competing pollutants) to a typical stable level (23-32%), depending on the coexistence of other pollutants and moisture in the air, that the employment of this type of filter might generate byproducts (opposite to previous literature reports), and that small-scale column tests represented a good indication for large-scale filter performance as a practical screening method.

Room-temperature catalytic oxidation of formaldehyde on catalysts

Room-temperature catalytic oxidative decomposition of harmful formaldehyde (HCHO) in indoor air is summarized.

Low temperature catalytic oxidation of volatile organic compounds: a review

Volatile organic compounds (VOCs) are toxic and recognized as one of the major contributors to air pollution.

Complete Benzene Oxidation over Colloidal Gold Catalysts Supported on Nanostructure Zinc Oxide

The catalytic activities of various nanometer metal oxides (ZnO, CeO2, ZrO2, Al2O3, Co3O4, MgO) supported colloidal gold catalysts with self-designed equipment were evaluated and compared for benzene catalytic oxidation. The results showed that ZnO was the most activive support of the colloidal gold among these nanometer metal oxides. The effects of Au/ZnO on the activity for benzene oxidation were investigated at 50- 300°C. The optimal gold loading was 2 wt%. The Au/ZnO was characterized using BET, XRD, and TEM methods. The XRD patterns and TEM image showed that gold nanoparticles were well dispersed on the surface of ZnO, and the mean diameter was 3.1±0.81 nm. The gaseous products of benzene oxidation and the adsorbed species on Au/ZnO catalyst surface were characterized with FTIR and GC-MS. It was proved that benzene was completely oxidized into CO2 and H2O over the Au/ZnO catalyst at low temperature.

Gold catalysis

Catalysis by gold has rapidly become a hot topic in chemistry, with a new discovery being made almost every week. Gold is equally effective as a heterogeneous or a homogeneous catalyst and in this Review we attempt to marry these two facets to demonstrate this new found and general efficacy of gold. The latest discoveries are placed within a historical context, but the main thrust is to highlight the new catalytic possibilities that gold-catalyzed reactions currently offer the synthetic chemist, in particular in redox reactions and nucleophilic additions to pi systems. Indeed gold has proved to be an effective catalyst for many reactions for which a catalyst had not been previously identified, and many new discoveries are still expected.