Yanqiang Huang

FeOx-supported platinum single-atom and pseudo-single-atom catalysts for chemoselective hydrogenation of functionalized nitroarenes

The catalytic hydrogenation of nitroarenes is an environmentally benign technology for the production of anilines, which are key intermediates for manufacturing agrochemicals, pharmaceuticals and dyes. Most of the precious metal catalysts, however, suffer from low chemoselectivity when one or more reducible groups are present in a nitroarene molecule. Herein we report FeOx-supported platinum single-atom and pseudo-single-atom structures as highly active, chemoselective and reusable catalysts for hydrogenation of a variety of substituted nitroarenes. For hydrogenation of 3-nitrostyrene, the catalyst yields a TOF of ~1,500 h(-1), 20-fold higher than the best result reported in literature, and a selectivity to 3-aminostyrene close to 99%, the best ever achieved over platinum group metals. The superior performance can be attributed to the presence of positively charged platinum centres and the absence of Pt-Pt metallic bonding, both of which favour the preferential adsorption of nitro groups.

A Noble-Metal-Free Catalyst Derived from Ni-Al Hydrotalcite for Hydrogen Generation from N2H4⋅H2O Decomposition†

Storing hydrogen safely and efficiently is one of the major technological barriers preventing the widespread application of hydrogen-fueled cells, such as proton exchange membrane fuel cells (PEMFCs). Hydrous hydrazine (N2H4·H2O) is considered as a promising liquid hydrogen storage material owing to the high content of hydrogen (7.9%) and the advantage of CO-free H2 produced. [1] In particular, hydrous hydrazine offers great potential as a hydrogen storage material for some special applications, such as unmanned space vehicles and submarine power sources, where hydrazine is usually used as a propellant. The decomposition of hydrazine proceeds by two typical reaction routes:

Catalytic conversion of cellulose to hexitols with mesoporous carbon supported Ni-based bimetallic catalysts

Robust and highly active Ni-based bimetallic catalysts supported on mesoporous carbon have been developed for catalytic conversion of cellulose to hexitols, over which the maximum hexitol yield reached 59.8%.

Design of a Highly Active Ir/Fe(OH)x Catalyst: Versatile Application of Pt‐Group Metals for the Preferential Oxidation of Carbon Monoxide

The proton-exchange membrane fuel cell (PEMFC) has been regarded as one of the most promising candidates for the efficient use of hydrogen energy. However, small amounts of CO (0.3–1%) in the H2 stream from reforming processes must be selectively removed because CO is highly poisonous to the Pt anode of a PEMFC. The preferential oxidation of CO in a H2-rich gas (PROX) is presently the most effective approach to address this problem. Oxide-supported Au catalysts are highly active for the PROX reaction even at room temperature, but the lower stability and sensitivity to CO2 constrain their practical applications. Supported Pt catalysts, on the other hand, are less active and only a few have shown reasonable activity for conversion of CO at temperatures lower than 60 8C. Therefore, it is highly desirable to develop improved catalysts with better catalytic performance for the PROX reaction at lower temperatures. Ir has a higher melting point and surface energy than other metals with 5f orbitals, such as Pt and Au, and Ir can be well-dispersed on and strongly interact with the support. However, compared to Ptand Au-based catalysts, Ir-based catalysts have limited applications in heterogeneous catalysis and are rarely investigated for the PROX reaction, most probably because of its inferior activity. Although much effort has been made to improve the activity of Ir-based catalysts and remarkable progress has been achieved, their activities for the PROX reaction are still low at low temperatures. In fact, there is no report so far claiming that Ir-based catalysts can show high activity at temperatures below 80 8C; thus it remains a formidable challenge to utilize Ir-based catalysts for the PROX reaction at ambient temperatures. One basic task of modern catalysis is to rationally design catalysts based on the fundamental understanding of their reaction mechanisms. Especially, the contribution of support materials to the performance of the final catalysts should be taken into account. For the PROX reaction, the strong binding of CO to Ir poisons the surface so that O2 cannot competitively adsorb on the Ir surface and be activated at low temperatures, thereby prohibiting the conversion of CO to CO2. Therefore, weakening the adsorption strength of CO and/or promoting the activation of O2 at lower temperatures have become the crucial steps. Ferric oxide has proven effective for O2 activation and has been used extensively as an additive to Pt-based catalysts. Recently, we have designed a bimetallic catalyst by adding FeOx to a supported Ir catalyst, and the activity for the PROX reaction was improved. Further study of the catalytic reactions showed that the reaction rate of CO oxidation correlated well with the presence and amount of Fe, suggesting that Fe sites were indeed the active sites for O2 activation. [13] The coordinatively unsaturated Fe center was also recently identified as the site to activate O2, which helped the design of a highly active FeOx/Pt/SiO2 catalyst to totally convert CO at room temperature. All of these studies suggest that the presence of low-valent Fe (Fe) played a decisive role in improving the PROX activity, thus providing a clue for obtaining a highly effective Ir-based catalyst by incorporating materials containing, or easily forming, Fe species. Ferric hydroxide (Fe(OH)x) is a novel support material which has recently been adopted to stabilize various types of metal species for CO oxidation. It possesses a large surface area and a large amount of OH groups; these unique properties make Fe(OH)x a good candidate for generating highly dispersed metal clusters or even single-atom catalysts. Furthermore, the longer Fe O bonds in Fe(OH)x (compared to those in Fe2O3) make it easier to form Fe 2+

A Schiff base modified gold catalyst for green and efficient H2 production from formic acid

Formic acid (FA) dehydrogenation is an atom-economic method for H2 production, while diluted FA with extra additives is generally required in heterogeneous dehydrogenation of FA. Here, we report a novel Schiff base functionalized gold catalyst, which showed excellent catalytic performances for H2 production in catalytic dehydrogenation of high-concentration FA without any additives. The record turnover frequency (TOF) was as high as 4368 h−1 in 10 M FA solutions, and was up to 2882 h−1 even in 99% FA at a mild temperature of 50 °C. According to characterization results, a synergetic mechanism for C–H activation between the protonated Schiff base and electronegative gold nanoparticles (NPs) at the interface was suggested to be responsible for its unusual catalytic activity toward H2 production from FA.

Aerobic oxidative coupling of alcohols and amines over Au–Pd/resin in water: Au/Pd molar ratios switch the reaction pathways to amides or imines

A facile switch of the reaction pathways of aerobic oxidative coupling of alcohols and amines from amidation to imination was realized for the first time by tuning the Au/Pd ratios in ion-exchange resin supported Au–Pd alloy catalysts (Au–Pd/resin). Amides were obtained with high yields on Au6Pd/resin while imines were obtained over AuPd4/resin. Various alcohols and amines underwent oxidative coupling smoothly in water to afford the desired products with good to excellent yields. Further investigation on the reaction mechanism suggested the synergistic effect between Au and Pd determined the adsorption strength of the aldehyde intermediate, which in turn dictated the reaction pathways. That is, on Au-rich alloys (e.g., Au6Pd) absorbed aldehyde species was formed, followed by further oxidation to yield amides, while on Pd-rich alloys (e.g., AuPd4), free aldehyde was generated, which then underwent condensation with amines to produce imines. The discovery might provide avenues to develop new efficient catalysts for the green synthesis of special chemicals.

CO2 Hydrogenation over Oxide-Supported PtCo Catalysts: The Role of the Oxide Support in Determining the Product Selectivity

By simply changing the oxide support, the selectivity of a metal-oxide catalysts can be tuned. For the CO2 hydrogenation over PtCo bimetallic catalysts supported on different reducible oxides (CeO2 , ZrO2 , and TiO2 ), replacing a TiO2 support by CeO2 or ZrO2 selectively strengthens the binding of C,O-bound and O-bound species at the PtCo-oxide interface, leading to a different product selectivity. These results reveal mechanistic insights into how the catalytic performance of metal-oxide catalysts can be fine-tuned.

Unique catalysis of Ni-Al hydrotalcite derived catalyst in CO2 methanation: cooperative effect between Ni nanoparticles and a basic support

Ni-Al hydrotalcite derived catalyst (Ni-Al2O3-HT) exhibited a narrow Ni particle-size distribution with an average particle size of 4.0 nm. Methanation of CO2 over this catalyst initiated at 225 degrees C and reached 82.5% CO2 conversion with 99.5% CH4 selectivity at 350 degrees C, which was much better than its impregnated counterpart. Characterizations by means of CO2 microcalorimetry and Al-27 NMR indicated that large amount of strong basic sites existed on Ni-Al2O3-HT, originated from the formation of Ni-O-Al structure. The existence of strong basic sites facilitated the activation of CO2 and consequently promoted the activity. The combination of highly dispersed Ni with strong basic support led to its unique and high efficiency for this reaction.

Promotional effect of Pd single atoms on Au nanoparticles supported on silica for the selective hydrogenation of acetylene in excess ethylene

A Pd single-atom alloy (SAA) structure was constructed by alloying Pd with Au supported on silica. The XRD and HRTEM results demonstrated that the addition of a small amount of Pd efficiently prevented the sintering of Au nanoparticles. The DRIFTS and EXAFS results confirmed that the Pd SAA structure was formed when the atomic ratios of Pd/Au were lower than 0.025. The Pd SAA structure exhibits a much better catalytic performance for the selective hydrogenation of acetylene in excess ethylene than the corresponding monometallic Au or Pd systems.

Palladium on Nitrogen-Doped Mesoporous Carbon: A Bifunctional Catalyst for Formate-Based, Carbon-Neutral Hydrogen Storage.

The lack of safe, efficient, and economical hydrogen storage technologies is a hindrance to the realization of the hydrogen economy. Reported herein is a reversible formate-based carbon-neutral hydrogen storage system that is established over a novel catalyst comprising palladium nanoparticles supported on nitrogen-doped mesoporous carbon. The support was fabricated by a hard template method and nitridated under a flow of ammonia. Detailed analyses demonstrate that this bicarbonate/formate redox equilibrium is promoted by the cooperative role of the doped nitrogen functionalities and the well-dispersed, electron-enriched palladium nanoparticles.