Boosting the catalytic performance of single-atom catalysts by tuning surface lattice expanding confinement.

A Ti3+-rich rutile TiO2 with a surface lattice expansion structure was constructed by H2 treatment, on which the supported Pt single atoms were stabilized in a highly oxidized state under a CO oxidation reaction atmosphere and had a weaker affinity for CO, thus exhibiting robust catalytic performance.

Ce-Si Mixed Oxide: A High Sulfur Resistant Catalyst in the NH3-SCR Reaction through the Mechanism-Enhanced Process.

Investigating catalytic reaction mechanisms could help guide the design of catalysts. Here, aimed at improving both the catalytic performance and SO2 resistance ability of catalysts in the selective reduction of NO by NH3 (NH3-SCR), an innovative CeO2-SiO2 mixed oxide catalyst (CeSi2) was developed based on our understanding of both the sulfur poisoning and reaction mechanisms, which exhibited excellent SO2/H2O resistance ability even in the harsh working conditions (containing 500 ppm of SO2 and 5% H2O). The strong interaction between Ce and Si (Ce-O-Si) and the abundant surface hydroxyl groups on CeSi2 not only provided fruitful surface acid sites but also significantly inhibited SO2 adsorption. The NH3-SCR performance of CeSi2 was promoted by an enhanced Eley-Rideal (E-R) mechanism in which more active acid sites were preserved under the reaction conditions and gaseous NO could directly react with adsorbed NH3. This mechanism-enhanced process was even further promoted on sulfated CeSi2. This work provides a reaction mechanism-enhanced strategy to develop an environmentally friendly NH3-SCR catalyst with superior SO2 resistance.

Gas phase sulfation of ceria-zirconia solid solutions for generating highly efficient and SO2 resistant NH3-SCR catalysts for NO removal.

A series of ceria-zirconia solid solutions (CexZr1-xO2) were prepared by co-precipitation method and then sulfated with SO2 + O2 at 200 °C. Subsequent testing with the selective catalytic reduction of NO by NH3 (NH3-SCR) showed that the activity of the sulfated CexZr1-xO2 catalysts oxide catalysts exhibited a volcano-type tendency with increasing Zr content. Furthermore, the sulfated Ce0.6Zr0.4O2 catalyst showed the most desirable NH3-SCR activity at 250-300 °C, and exhibited much better SO2 resistance at 250 °C. Detailed characterization results demonstrated that Ce0.6Zr0.4O2 could adsorb more surface sulfate species and then produce more stable acid sites than pure CeO2 at 200 °C. After sulfation treatment, more Ce3+ and oxygen vacancies were formed on the surface of Ce0.6Zr0.4O2. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) experiments suggested that the nitrates species deposited on the surface of as-prepared Ce0.6Zr0.4O2, which showed no reactivity, could barely deposit on the same sample after sulfation. While, the sulfated Ce0.6Zr0.4O2 had more reactive acid sites to participate in the NH3-SCR and the reaction proceeded via Eley-Rideal mechanism. This work proved that sulfation treatment could be used in designing an efficient cerium-zirconium based NH3-SCR catalyst with great application prospect.

Insights into the precursor effect on the surface structure of γ-Al2O3 and NO + CO catalytic performance of CO-pretreated CuO/MnOx/γ-Al2O3 catalysts.

NO reduction by CO was investigated over CO-pretreated CuO/MnOx/γ-Al2O3 catalysts with different metal precursors (nitrate and acetate). It was found that the catalyst prepared from acetate salts (Cu/Mn/Al-A) exhibited significantly higher activity than counterpart catalyst from nitrate precursors (Cu/Mn/Al-N). XRD, XPS and in situ DRIFT were carried out to approach the nature for the different catalytic performance. For both catalysts, copper mainly existed as CuO, but the status of manganese oxide was markedly different. Mn(IV) was predominant in Cu/Mn/Al-N and Mn(III) was enriched in Cu/Mn/Al-A. As a result, different dispersion behaviors of manganese oxide on γ-Al2O3 were displayed, which induced inconsistent Cu-Mn contact. The catalyst obtained from acetate precursor exhibited enriched Cu-Mn contact and thus more Cu+-□-Mn3+/2+ entities would be produced after CO pretreatment, leading to promoted NO dissociation and favorable performance in NO reduction by CO. The present study sheds light on the effective tuning of Cu-O-Mn interfacial sites in CuO/MnOx/γ-Al2O3 via modulating the dispersion behaviors of surface components.

Ultrafine Bi3TaO7 Nanodot-Decorated V, N Codoped TiO2 Nanoblocks for Visible-Light Photocatalytic Activity: Interfacial Effect and Mechanism Insight.

Bi3TaO7 is a potential photocatalyst because of its high chemical stability, defective fluorite-type structure, and superior mobility of photoinduced holes. However, few studies have focused on the interfacial effects of Bi3TaO7-based photocatalysts. In this work, 0D Bi3TaO7 nanodot-hybridized 3D V and N codoped TiO2 nanoblock (B/VNT) composites were first synthesized for the photocatalytic removal of oxytetracycline hydrochloride, 2,4,6-trichlorophenol, and tetrabromobisphenol A. The fabricated B/VNT had a photocatalytic performance superior to that of pristine components, and probable degradation pathways were proposed according to the primary intermediates identified by a gas chromatography-mass spectrometer. Interestingly, on B/VNT, the transfer of interfacial electrons was observed from V/N-TiO2 to Bi3TaO7, and the formed built-in electronic field led to a direct Z-scheme structure, rather than type II, as confirmed by the generated •OH and •O2- radicals and band structures from the density functional theory calculation. Therefore, the strong interfacial electronic interaction on the B/VNT was significant, which drove faster photogenerated charge transfer, more visible-light adsorption, and active •OH and •O2- generation, thus improving the photocatalytic activity.

Pore Size Expansion Accelerates Ammonium Bisulfate Decomposition for Improved Sulfur Resistance in Low-Temperature NH3-SCR.

Sulfur poisoning has long been recognized as a bottleneck for the development of long-lived NH3-selective catalytic reduction (SCR) catalysts. Ammonium bisulfate (ABS) deposition on active sites is the major cause of sulfur poisoning at low temperatures, and activating ABS decomposition is regarded as the ultimate way to alleviate sulfur poisoning. In the present study, we reported an interesting finding that ABS decomposition can be simply tailored via adjusting the pore size of the material it deposited. We initiated this study from the preparation of mesoporous silica SBA-15 with uniform one-dimensional pore structure but different pore sizes, followed by ABS loading to investigate the effect. The results showed that ABS decomposition proceeded more easily on SBA-15 with larger pores, and the decomposition temperature declined as large as 40 °C with increasing pore size of SBA-15 from 4.8 to 11.8 nm. To further ascertain the real effect in NH3-SCR reaction, the Fe2O3/SBA-15 probe catalyst was prepared. It was found that the catalyst with larger mesopores exhibited much improved sulfur resistance, and quantitative analysis results obtained from Fourier transform infrared and ion chromatograph further proved that the deposited sulfates were greatly alleviated. The result of the present study demonstrates for the first time the vital role of pore size engineering in ABS decomposition and may open up new opportunities for designing NH3-SCR catalysts with excellent sulfur resistance.

Engineering the TiO2 -graphene interface to enhance photocatalytic H2 production.

In this work, TiO2 -graphene nanocomposites are synthesized with tunable TiO2 crystal facets ({100}, {101}, and {001} facets) through an anion-assisted method. These three TiO2 -graphene nanocomposites have similar particle sizes and surface areas; the only difference between them is the crystal facet exposed in TiO2 nanocrystals. UV/Vis spectra show that band structures of TiO2 nanocrystals and TiO2 -graphene nanocomposites are dependent on the crystal facets. Time-resolved photoluminescence spectra suggest that the charge-transfer rate between {100} facets and graphene is approximately 1.4 times of that between {001} facets and graphene. Photoelectrochemical measurements also confirm that the charge-separation efficiency between TiO2 and graphene is greatly dependent on the crystal facets. X-ray photoelectron spectroscopy reveals that Ti-C bonds are formed between {100} facets and graphene, while {101} facets and {001} facets are connected with graphene mainly through Ti-O-C bonds. With Ti-C bonds between TiO2 and graphene, TiO2 -100-G shows the fastest charge-transfer rate, leading to higher activity in photocatalytic H2 production from methanol solution. TiO2 -101-G with more reductive electrons and medium interfacial charge-transfer rate also shows good H2 evolution rate. As a result of its disadvantageous electronic structure and interfacial connections, TiO2 -001-G shows the lowest H2 evolution rate. These results suggest that engineering the structures of the TiO2 -graphene interface can be an effective strategy to achieve excellent photocatalytic performances.