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Summary Ammonia synthesis is structure sensitive, and a minute change in the catalyst structure would cause a dramatic change in activity. To date, none of the studies reveal the metal size effect at a subnanometer scale on NH3 synthesis, and such investigation remains a challenge. Here, we report the synthesis of Ru catalysts with sizes ranging from single atoms, atomic clusters (ACCs), sub-nanometric clusters, to nanoparticles (NPs) by adjusting precursor and/or loading of Ru. Sub-nanometric Ru catalysts not only exhibit performance different from that of NPs but also follow a different route for N2 activation. The strong intra-cluster interaction of Ru atomic clusters enables the formation of strong interactions of Ru d-orbitals with the σ and π orbitals of N2 molecules, resulting in N2 activation over Ru ACCs to occur more easily than that over Ru NPs. Consequently, Ru ACCs display an unprecedentedly high NH3 synthesis rate and large turnover frequency at mild conditions.

Identifying optimal Ru size in NH3 synthesis can improve reaction activity and maximize the utilization of Ru to reduce catalyst cost. However, previous researches are focused on large Ru particle size (≥ 2 nm) while that below 2 nm in NH3 synthesis is unclear. Here we synthesized a series of Rux/BaCeO3 with different Ru sizes (x=1.1–3.0 nm) through size-controlled Ru colloid. With the decrease of Ru size, NH3 synthesis rate over Ru1.1/BaCeO3 increases to 19.4 mmol gcat−1 h−1 at 400°C and 1 MPa, which is 5.7 times that of Ru3.0/BaCeO3 and superior to most of Ru-based catalysts previously reported. It reveals that the reduction of Ru size enhances the generation of Ce3+ and oxygen vacancies in BaCeO3, which can donate electron to Ru centers and promote N2 dissociation. Moreover, the small Ru size enhances hydrogen spillover from Ru to BaCeO3 to alleviate hydrogen poisoning, resulting in efficient NH3 synthesis.

It is known that a highly dynamic communication among subcellular organelles (e.g., cytosol, endoplasmic reticulum (ER), mitochondria, and nucleus) dictate cellular behaviors. But little information exists on how the inter-organelle crosstalk impacts cancer cells due to the lack of approaches that manipulate inter-organelle communication in cancer cells. We unexpectedly found that a negatively charged, enzyme cleavable peptide enables the trafficking of histone protein (H2B), a nuclear protein, to the mitochondria in cancer cells. The peptide, denoted as MitoFlag, interacts with the nuclear location sequence (NLS) of H2B to block it entering nucleus. A protease on the mitochondria cleaves the Flag from the complex of MitoFlag and H2B to form assemblies that retain H2B on the mitochondria and facilitate the H2B entering mitochondria. Molecular validation of MitoFlag shows that adding NLS, replacing aspartic acid residues by glutamic acid residues, or changing L-aspartic acid to D-aspartic residue abolishes the trafficking of H2B into mitochondria of HeLa cells. As the first example of enzyme-instructed self-assembly (EISA) of a synthetic peptide for trafficking endogenous proteins, this work provides insights for understanding and manipulating inter-organelle communication in cells.

A series of CoMgAl mixed oxides with homogeneous Co dispersion were prepared using co-precipitation method. The CoMgAl composites were then doped with Mo species, giving Mo/Co(x)MgAl (x=Co/(Co+Mg)) catalysts for water-gas shift reaction (WGSR). In the synthesis of these catalysts, there is limited release of ammonia, which is traditionally common in the generation of Mo-Co catalysts for WGSR. The Mo/Co(x)MgAl catalysts were characterized using techniques such as XRD, N2-physisorption, H2-TPR, H2S-TPS, Raman, HRTEM and XPS. It is noted that the Mo/Co(5%)MgAl catalyst gives 91.2% CO conversion at 350 °C, which is close to the equilibrium CO conversion (91.7%). The H2S-TPS results disclose that there is decrease in activation energy for Mo sulfidation with increase of Co content in Mo/Co(x)MgAl, indicating the presence of Co promotes Mo sulfidation. The outcomes of HRTEM and XPS analyses reveal that the role of Co is to decrease stacking number and slab length of MoS2 moieties. The EDX elemental analysis suggests synergism between Co and MoS2, especially in the case of Mo/Co(5%)MgAl. With the formation of small-size MoS2 slabs and enhanced Co-MoS2 synergistic effect, the Mo/Co(5%)MgAl catalyst has high exposure of active sites, leading to improved catalytic activities in WGSR.

The alloying of Ru with rare-earth elements (REEs) is an effective approach for the modification of the electronic structure of Ru. Here, for the first time, we report the formation of Ru-M (M=La or Y) alloys that are endowed with a completely new type of active sites. Over the Ru-M (M=La or Y) catalysts, N2 activation in ammonia synthesis follows neither the well-known dissociative nor the associative route but rather a co-operation of both, leading to outstanding performance. The developed RuLa/HZ catalyst exhibits a NH3 synthesis rate of 14.73 mmol gcat−1 h−1 at 400 °C and 1 MPa without obvious deactivation in a run of 1756 h (ca.73 days).

A series of Mg-Al-Ce mixed oxides with (nMg2+)/(nCe3+ + nAl3+) = 5 and nCe3+/(nCe3+ + nAl3+) = 0 ∼ 7% were synthesized by co-precipitation method based on a hydrotalcite route and used as support to prepare Co-Mo sulfur-resistant water-gas shift (WGS) catalysts. The supports and catalysts were characterized by XRD, ICP, N2-physisorption, CO2-TPD, H2-TPR, H2S-TPS, TEM, and CO-IR. It is found that the catalytic performance and physicochemical property of the Co-Mo/Mg(Al)O catalyst are significantly influenced by the Ce modification. The addition of Ce effectively enhances the WGS activity and the highest activity is obtained on the Co-Mo/Mg(Al)O-CeO2 (5%) catalyst, where the activity at 623 K increases about 2.5 times. The results of H2S-TPS investigation show that in the presence of Ce, the H2S consumption peak shifts to lower temperatures and there is decrease of Mo sulfidation activation energy. Furthermore, HRTEM analysis shows that the addition of Ce (5%) results in decrease of MoS2 slab length and stacking number, and those of CO-IR characterization indicate increased exposure of surface MoS2 sites. It is suggested that the addition of Ce promotes the formation of MoS2 slabs that are smaller in size, leading to higher exposure of surface active sites and hence higher activity.

Ru catalysts (2 wt%) supported on Mg and/or Al oxides including γ-Al 2 O 3 , MgAl 2 O 4 , Mg 3 (Al)O, and MgO were prepared by incipient wetness impregnation and compared for the CH 4 -CO 2 reforming to investigate the effect of support on the Ru dispersion and catalytic performance. The catalysts before and after reaction were well characterized by using N 2 physical adsorption, ICP, SEM-EDX, XRD, H 2 -TPR, TEM, CO chemisorption, FTIR of CO adsorption, XPS, CO 2 -TPD, TG, and Raman spectroscopy. The characterization results revealed that Ru metal was very highly dispersed on the Mg 3 (Al)O mixed oxide obtained from Mg-Al layered double hydroxide, probably existing in very small nanoparticles and/or clusters. The order of Ru metal dispersion was Ru/Mg 3 (Al)O > Ru/MgO > Ru/MgAl 2 O 4 > Ru/γ-Al 2 O 3 . The catalytic activity and stability of the Ru catalysts were greatly dependent on the support. Both Ru/MgO and Ru/Mg 3 (Al)O showed higher activity than Ru/MgAl 2 O 4 and Ru/γ-Al 2 O 3 , which might be related to the strong base intensity of support and more accessible surface Ru 0 atoms, respectively. During 30 h of reaction at 1023 K, a significant deactivation occurred on Ru/γ-Al 2 O 3 , Ru/MgAl 2 O 4 , and Ru/MgO, which was mainly attributed to the sintering of Ru metal particles. In contrast, the Ru/Mg 3 (Al)O catalyst exhibited superior stability and no significant sintering of Ru metal was observed, suggesting that the highly dispersed Ru metal was stable. A 300 h long-term test further demonstrated the excellent stability of Ru/Mg 3 (Al)O. These results highlight the significant effect of Mg(Al)O mixed oxide on the improvement of Ru dispersion and catalytic performance, and this might be related to the unique properties of Mg(Al)O mixed oxide including memory effect, low crystallinity, and its strong interaction with Ru.

A novel configuration of porous ZnO/Sn1−xZnxO2−x heterojunction nanocatalyst with high photocatalytic activity was successfully synthesized through a simple two-step solvothermal method. Porous Sn1−xZnxO2−x was synthesized from Zn2+ and Sn4+ precursors with the Zn/Sn ratio of 2:1 in the absence of alkali, and then intermolecular dehydrolysis led to the formation of heterointerface between Sn1−xZnxO2−x and ZnO. The results show that Zn2+ doping exhibits a significant influence on particle size of SnO2 leading to much higher specific surface area and larger band gap, which is in favor of the photocatalytic activity of SnO2 under UV light irradiation. In addition, the formation of ZnO/Sn1−xZnxO2−x heterostructure improves the separation of photogenerated electron–hole pairs due to the potential difference between Sn1−xZnxO2−x and ZnO, which also benefits to photocatalysis. By taking account of them together, these results provide further insight into the synergistic effects of metal ion doping and semiconductor/semiconductor heterostructure on the activity of photocatalysts in environmental remediation applications.

Au/ZrO2 catalysts with a nominal gold loading of 1.0% were prepared by a deposition-precipitation method employing a series of ZrO2 samples synthesized by a convenient hydrothermal route as supports. These catalysts were evaluated for low-temperature water-gas shift reaction under a model reformed methanol gas atmosphere. The effect of the hydrothermal synthesis temperature of zirconia on the catalytic activity of Au/ZrO2 was investigated. The optimal hydrothermal synthesis temperature of ZrO2 was 150 °C. The corresponding catalyst offers a CO conversion of 87% at a reaction temperature of 240 °C, which is significantly higher than that of the previously reported Au/Fe2O3, Au/CeO2, and Au/CeZrO4 catalysts. The Au/ZrO2 catalysts were characterized by X-ray diffraction, atomic absorption spectrometry, N2-physisorption, and scanning electron microscopy. The results indicate that the catalytic performance of the Au/ZrO2 catalysts is mainly influenced by the morphology and pore structure of the ZrO2 that was hydrothermally synthesized at different temperatures. A uniform nanodisk morphology and increase in the pore volume and pore diameter of the ZrO2 particles lead to a higher catalytic activity of the Au/ZrO2 catalyst.

The water-gas shift reaction was used to evaluate a series of La2O3 modified CuO/CeO2 catalysts that were prepared by a parallel co-precipitation method. The catalytic activity and thermal stability improved significantly upon the introduction of La2O3, and CuO/CeO2-La2O3 (2 wt%) gave the highest activity and had the best thermal stability. The microstructure of the as-prepared CuO/CeO2-La2O3 catalysts and/or the CeO2-La2O3 supports was characterized by X-ray diffraction, N2 physisorption, Raman spectroscopy, and temperature-programmed reduction. The results indicate that larger specific surface areas and smaller crystal sizes of CuO and CeO2 result in improved catalytic performance for the as-prepared catalysts. Moreover, the incorporation of La3+ into the ceria lattice promotes the generation of oxygen vacancies leading to a higher number of moderate copper oxides that interact with surface oxygen vacancies on the surface of the ceria. This enhances the activity and thermal stability of the CuO/CeO2 catalyst.

Copper supported on ceria prepared by the impregnation method was used as a model catalyst to investigate the synergetic mechanism between copper species and ceria for NO reduction by CO. To identify the copper species in the catalyst, we treated the as-synthesized Cu/CeO 2 by 30 wt.% nitric acid solution. Fresh and nitric acid treated Cu/CeO 2 catalysts were characterized and compared with AAS, XRD, TPR, EPR, Raman and NO-TPD techniques. It is found that, after nitric acid treatment, there is only 0.27 wt.% Cu left (vs. 5 wt.% Cu in fresh sample); this is present in the following forms: (1) isolated copper ions in octahedral sites of ceria, (2) copper oxide clusters and (3) copper ions in ceria lattice. The residual small amount of Cu has a significant effect on surface structure, redox property and catalytic behavior of ceria, indicating that these copper species are crucial copper species inducing copper–ceria interactions. Moreover, it is suggested that the relative free movement of oxygen from ceria to supported copper, caused by the three copper species, leads to oxygen vacancies in ceria, significantly enhancing the NO conversion of Cu/CeO 2 during NO + CO reaction.

Copper supported on ceria and ceria-magnesia catalysts were synthesized and used for NO reduction by CO. The supports and the subsequent Cu catalysts were prepared by citric acid sol–gel and impregnation methods, respectively. Based on XRD, TPR and EPR measurements, it is found that the Mg addition promotes not only the dispersion of CuO, but also the doping of copper ions into CeO 2 matrix. A redox treatment favors some of copper ions in the octahedral sites of CeO 2 substituting the lattice sites of Ce 4+ . Combining the results of activity test, we found that the formation of copper-substituted Cu-O-Ce solid solution promotes the catalytic activity of the catalysts. Also, the ways that MgO acts on the dispersion of CuO and the formation of Cu-O-Ce solid solutions were investigated with the aid of TEM, TGA and XRD techniques. The results of these studies suggest that magnesia crystallites undergo a phase evolvement during the preparation process of Cu/MgO-CeO 2 , leading to the reconstitution of the support and hence the improvement of copper dispersion, BET surface area, pore volume, as well as the doping of copper ions into the CeO 2 matrix.

A series of Au/Fe 2 O 3 catalysts for the water gas shift (WGS) reaction were prepared by modified deposition-precipitation method. The sample calcined at 300 °C showed higher catalytic activity and better stability than other samples. Using N 2 physisorption, in situ XRD, H 2 -TPR, and XPS techniques, the influence of calcination temperature on properties of Au/Fe 2 O 3 catalyst was explored, and the cause of deactivation was analyzed as well. The results showed that the catalytic behaviors were related to the interaction between Au and Fe 2 O 3 , and the reductive property of support, both of which were significantly affected by calcination temperature. Furthermore, according to the results of XPS, although stable carbonate and carbonyl surface species were found on the spent catalysts, the semiquantitative analysis of these species indicated that they were not the main cause of the deactivation. In fact, the deactivation of Au/Fe 2 O 3 was sensitive to the structure change of support. During the water gas shift reaction, Fe 3 O 4 particle would aggregate and crystallize leading to increase in the crystallinity of support and a significant reduction in the surface area of the catalysts, which resulted in the deactivation of Au/Fe 2 O 3 .

This paper reports a study on the influence of calcination temperature on the catalytic behavior of the Au/iron oxide systems in the water–gas shift reaction. The catalytic activity has been found to be strongly dependent on the catalyst pretreatment, decreasing on increasing the calcination temperature. Detailed characterization of the uncalcined and the calcined sample at different temperatures, employing BET analysis, XRD, H 2 -TPR, HRTEM and XPS, has shown that the catalytic behavior is related to the gold state and/or the particle size and the properties and structure of iron oxide support. Both the oxidation state and dispersion of gold and the phase transition and its crystallinity and reductive property of the support exert great influence on the catalytic performance of the gold/metal oxide. The wave of the activity within the middle reaction temperature range (i.e. 523–623 K) could be attributed to the difference of the operating temperatures belonging to the gold species and the active magnetite phase.