Xiaoli Pan

Strong Metal-Support Interactions between Gold Nanoparticles and Nonoxides.

The strong metal-support interaction (SMSI) is of great importance for supported catalysts in heterogeneous catalysis. We report the first example of SMSI between Au nanoparticles (NPs) and hydroxyapatite (HAP), a nonoxide. The reversible encapsulation of Au NPs by HAP support, electron transfer, and changes in CO adsorption are identical to the classic SMSI except that the SMSI of Au/HAP occurred under oxidative condition; the opposite condition for the classical SMSI. The SMSI of Au/HAP not only enhanced the sintering resistance of Au NPs upon calcination but also improved their selectivity and reusability in liquid-phase reaction. It was found that the SMSI between Au and HAP is general and could be extended to other phosphate-supported Au systems such as Au/LaPO4. This new discovery may open a new way to design and develop highly stable supported Au catalysts with controllable activity and selectivity.

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.

Hydrogenolysis of Glycerol to 1,3-propanediol under Low Hydrogen Pressure over WOx -Supported Single/Pseudo-Single Atom Pt Catalyst.

Single/pseudo-single atom Pt catalyst was prepared on mesoporous WOx . The large surface area and abundant oxygen vacancies of WOx improve the Pt dispersion and stabilize the Pt isolation. This newly prepared catalyst exhibited outstanding hydrogenolysis activity under 1 MPa H2 pressure with a very high space-time yield towards 1,3-propanediol (3.78 g gPt (-1)  h(-1) ) in Pt-W catalysts. The highly isolated Pt structure is thought to contribute to the excellent H2 dissociation capacity over Pt/WOx . The high selectivity towards 1,3-propanediol is attributed to the heterolytic dissociation of H2 at the interface of Pt and WOx (providing specific Brønsted acid sites and the concerted dehydration-hydrogenation reaction) and the bond formation between glycerol and WOx , which favors/stabilizes the formation of a secondary carbocation intermediate as well as triggers the redox cycle of the W species (W(6+) ⇄W(5+) ).

ZnAl‐Hydrotalcite‐Supported Au25 Nanoclusters as Precatalysts for Chemoselective Hydrogenation of 3‐Nitrostyrene

Chemoselective hydrogenation of 3-nitrostyrene to 3-vinylaniline is quite challenging because of competitive activation of the vinyl group and the nitro group over most supported precious-metal catalysts. A precatalyst comprised of thiolated Au25 nanoclusters supported on ZnAl-hydrotalcite yielded gold catalysts of a well-controlled size (ca. 2.0 nm)-even after calcination at 500 °C. The catalyst showed excellent selectivity (>98 %) with respect to 3-vinylaniline, and complete conversion of 3-nitrostyrene over broad reaction duration and temperature windows. This result is unprecedented for gold catalysts. In contrast to traditional catalysts, the gold catalyst is inert with respect to the vinyl group and is only active with regard to the nitro group, as demonstrated by the results of the control experiments and attenuated total reflection infrared spectra. The findings may extend to design of gold catalysts with excellent chemoselectivity for use in the synthesis of fine chemicals.

Selective Hydrogenolysis of Glycerol to 1,3‐Propanediol: Manipulating the Frustrated Lewis Pairs by Introducing Gold to Pt/WOx

A highly dispersed Au and Pt catalyst supported on WOx was developed for high performance in the selective hydrogenolysis of glycerol to 1,3-propanediol (1,3-PD) under very mild reaction conditions (81.4 % glycerol conversion, 51.6 % 1,3-PD selectivity at 413 K, 1 MPa H2 ). The highly dispersed Au decreased the original surface Lewis-acid sites on Pt/WOx but greatly increased its in situ generated Brønsted-acid sites with the assistance of H2 through the formation of frustrated Lewis pairs. These in situ formed and spatially separated pairs of H+ and H- function as the active sites in glycerol conversion to 1,3-PD.

Pd/ZnO catalysts with different origins for high chemoselectivity in acetylene semi-hydrogenation

The heterogeneity of active sites is the main obstacle for selectivity control in heterogeneous catalysis. Single atom catalysts (SACs) with homogeneous isolated active sites are highly desired in chemoselective transformations. In this work, a Pd1/ZnO catalyst with single-atom dispersion of Pd active sites was achieved by decreasing the Pd loading and reducing the sample at a relatively low temperature. The Pd1/ZnO SAC exhibited excellent catalytic performance in the chemoselective hydrogenation of acetylene with comparable chemoselectivity to that of PdZn intermetallic catalysts and a greatly enhanced utilization of Pd metal. Such unusual behaviors of the Pd1/ZnO SAC in acetylene semi-hydrogenation were ascribed to the high-valent single Pd active sites, which could promote electrostatic interactions with acetylene but restrain undesired ethylene hydrogenation via the spatial restrictions of σ-chemical bonding toward ethylene.

Selective Production of Toluene from Biomass‐Derived Isoprene and Acrolein

Toluene is a basic chemical that is currently produced from petroleum resources. In this paper, we report a new route for the effective synthesis of toluene from isoprene and acrolein, two reactants readily available from biomass, through a simple two-step reaction. The process includes Diels-Alder cycloaddition of isoprene and acrolein in a Zn-containing ionic liquid at room temperature to produce methylcyclohex-3-enecarbaldehydes (MCHCAs) as intermediates, followed by M (M=Pt, Pd, Rh)/Al2 O3 -catalyzed consecutive dehydrogenation-decarbonylation of the MCHCAs at 573 K to generate toluene with an overall yield up to 90.7 %. Model reactions indicated that a synergistic inductive effect of the C=C double bond and the aldehyde group in MCHCA plays a key role in initiating the consecutive dehydrogenation-decarbonylation, and that methyl benzaldehydes are the key intermediates in the gas-phase transformation of MCHCAs. Microcalorimetric adsorption of CO on different catalysts showed that decarbonylation of the substrate occurs more likely on the strong adsorption sites. To the best of our knowledge, it is the first report of Pt/Al2 O3 -catalyzed consecutive dehydrogenation-decarbonylation of a given compound in one reactor. This work provides a highly efficient and environmental friendly route to toluene by utilizing two compounds that can be prepared from biomass.

In situ encapsulation of iron(0) for solar thermochemical syngas production over iron-based perovskite material

Methane-to-syngas conversion plays an important role in industrial gas-to-liquid technologies, which is commercially fulfilled by energy-intensive reforming methods. Here we present a highly selective and durable iron-based La0.6Sr0.4Fe0.8Al0.2O3-δ oxygen carrier for syngas production via a solar-driven thermochemical process. It is found that a dynamic structural transformation between the perovskite phase and a Fe0@oxides core–shell composite occurs during redox cycling. The oxide shell, acting like a micro-membrane, avoids direct contact between methane and fresh iron(0), and prevents coke deposition. This core–shell intermediate is regenerated to the original perovskite structure either in oxygen or more importantly in H2O–CO2 oxidant with simultaneous generation of another source of syngas. Doping with aluminium cations reduces the surface oxygen species, avoiding overoxidation of methane by decreasing oxygen vacancies in perovskite matrix. As a result, this material exhibits high stability with carbon monoxide selectivity above 95% and yielding an ideal syngas of H2/CO ratio of 2/1.Iron-based oxides are promising oxygen carriers for thermochemical syngas production, but can be prone to deactivation during the reaction. Here an iron-based catalyst is shown to transform reversibly between perovskite and core–shell structures during methane-to-syngas conversion, accounting for its high stability toward coke deposition.