负载于二氧化硅上的小尺寸氧化亚铜物种促进丙烯选择性氧化生成丙烯醛

氧化物负载的含铜材料是丙烯选择性氧化制备丙烯醛的理想催化剂,一直以来都受到人们的广泛关注.然而,对于该催化体系的结构与性能之间的关系仍不是很清楚.因此,我们以碳酸钠为沉淀剂,通过沉积沉淀法将铜负载于高比表面的二氧化硅载体上,从而得到了均匀分散且小尺寸的Cu/SiO2催化剂.另外,采用浸渍法制得了相同负载量的分散不均匀、大尺寸的Cu/SiO2催化剂.丙烯选择性氧化反应活性测试发现,沉积沉淀法制备的催化剂比浸渍法制备的更有利于丙烯醛的生成,表现出了优异的催化性能:在300℃反应时,丙烯的转化率达到25.5%,丙烯醛的选择性达到66.8%,对应的丙烯醛的生成速率高达10.5 mmol·h^-1·gcat.^-1或111.2 mmol·h^-1·gCu^-1,远远超出了浸渍法制备的催化剂性能(1.7 mmol·h^-1·gcat.^-1或17.2mmol·h^-1·gCu^-1)和文献中报道的结果.结合高角度环形暗场扫描透射电子显微镜(HAADF-STEM)和X射线吸收精细结构(XAFS)技术,对沉积沉淀法制备的催化剂进行表征,发现在反应后铜物种的结构发生了明显的变化,由小尺寸的氧化铜(CuO)团簇转变为氧化亚铜(Cu2O)团簇,并且铜物种的尺寸没有明显的增大.为了进一步探索铜物种在预处理(氢气还原)以及催化反应时(丙烯+氧气)的结构变化,对不同方法合成的两种催化剂进行了原位X射线粉末衍射测试,发现不同尺寸的铜物种在还原和反应时都经历了从氧化铜(CuO)变为金属Cu再到Cu2O的结构变化,并且Cu2O在320 min的反应过程中可以稳定存在,说明它是该催化反应的活性物种.另外,通过原位双光束傅里叶变换红外光谱追踪反应时气体分子在催化剂表面的吸脱附状态,发现丙烯可以有效地吸附在小尺寸Cu/SiO2催化剂表面,随着Cu2O的形成,检测到了烯丙基中间体(CH2=CHCH2*)的产生,该物种可以与邻近Cu2O上的一个氧发生反应,从而生成丙烯醛,因此结合N2O滴定实验,我们可认为,高度分散的小尺寸的Cu2O物种是丙烯进行高效选择性氧化反应生成丙烯醛的活性物种.

Transition metal nanoparticles supported La-promoted MgO as catalysts for hydrogen production via catalytic decomposition of ammonia

The uniformly dispersed transition metal(Co, Ni and Fe) nanoparticles supported on the surface of La-promoted Mg O were prepared via a deposition-precipitation method for hydrogen production from catalytic decomposition of ammonia. X-ray diffraction, N2 adsorption-desorption, transmission electron microscopy, temperature-programmed reduction and temperature-programmed desorption were used to investigate the structure-activity relation of catalysts in NH3 decomposition. The results show that the strong interaction between active species and support can effectively prevent the active species from agglomerating during ammonia decomposition reaction. In addition, the introduction of La species not only facilitates the adsorption and decomposition of NH3 and desorption of N2, but also benefits the better dispersion of the active species. The prepared catalysts showed very high catalytic activity for ammonia decomposition compared with the same active composition samples that reported previously. Meanwhile, the catalysts showed excellent high-temperature stability and no any deactivation was observed, which are very promising candidates for the decomposition of ammonia to hydrogen.

Ensemble of single-atom catalysis and defect engineering in Cu_(1)/CeO_(2) nanozymes for tumor therapy

As a class of nanomaterials with natural enzyme-like characteristics, nanozymes have shown their great potential in various applications. Reducible metal oxides featured with defect structures, and single-atom catalysts with isolated metal sites are regarded as two of the most promising nanozymes. However, the strategies to construct highly performed nanozymes by combining these advantages are rarely reported. Herein, we report the coordination-unsaturated single-atomic Cu species supported on sintered CeO_(2), which combines the advantages of defect engineering and single-atom catalysis, exhibiting a largely enhanced peroxidase(POD)-like activity. The high-temperature calcination induces the transformation of inert Cu_(1)O_(4) species into coordination-unsaturated Cu_(1)O_(3) sites. This novel Cu_(1)O_(3) active sites with an unsaturated coordination work as a new type of defect sites to greatly activate the isolated Cu atoms and accelerate the dissociation of H_(2)O_(2) to form hydroxyl radicals(·OH). The obtained nanozyme with a high POD-like activity possesses low cytotoxicity, showing potential applications for the tumor inhibition in vitro and in vivo.

Iron-based composite nanostructure catalysts used to produce COx-free hydrogen from ammonia

有裸体的铁范围上的壳涂层成功地被综合并且过去常催化氨分解的 ceria 或 titania 的基于铁的合成 nanostructures。新鲜、使用的催化剂的结构和质地被传播电子显微镜学描绘， X 光检查衍射在 situ X 光检查衍射，由氢的规划温度的减小，和 N 2 adsorptiondesorption。为氨分解，与铈和钛涂的基于铁的合成催化剂与裸体的铁范围催化剂相比显示出优秀催化活动，与产出将近 100 的前者 ? 在 650 点的 % 氨变换吗？

Facile Synthesis of Stable MO2N Nanobelts with High Catalytic Activity for Ammonia Decomposition

In the present work,high quality γ-Mo2N catalysts for ammonia decomposition were successfully synthesized via temperature programmed nitridation of α-MoO3 nanobelts.The optimal conditions for the synthesis of MoO3 precursors were obtained by using the orthogonal experimental method.The MoO3 precursors and the corresponding fresh and used Mo2N catalysts were characterized by various characterization techniques,including transmission electron microscopy,X-ray diffraction and N2 adsorption-desorption.Furthermore,temperature-programmed desorption by N2 or NH3 and X-ray photoelectron spectroscopy analysis were performed to better understand the chemical properties of Mo2N catalysts.The results revealed that Mo2N catalyst has good NH3 adsorption ability and facilitates the dissociation adsorption of N2.Moreover,the morphology and structure of Mo2N catalysts well maintained after the reaction.Therefore,among the three transition metal nitrides(Mo2N,W2N and VN)and some Mo-based catalysts previously reported,Mo2N catalysts showed very high activity and stability.Nearly 94% con version of NH3 could be reached at 550 ℃ with the gas hourly space velocity of 22 000 cm^3-gcat^-1·h^-1 and no obvious deactivation was observed during a 72 h test.

Promoted porous Co_3O_4-Al_2O_3 catalysts for ammonia decomposition

Transition metal catalysts have been considerably used for NH_3 decomposition because of the potential application in CO_x-free H_2 generation for fuel cells.However,most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components.Here,we adopted an efficient method,aerosol-assisted selfassembly approach(AASA),to prepare the optimized cobalt-alumina(Co_3O_4-Al_2O_3)catalysts.The Co_3O_4-Al_2O_3catalysts exhibited excellent catalytic performance in the NH_3 decomposition reaction,which can reach 100%conversion at 600°C and maintain stable for 72 h at a gaseous hourly space velocity(GHSV)of 18000 cm^3g^(-1)_(cat)h^(-1).The catalysts were characterized by various techniques including transmission electron microscope(TEM),scanning electron microscope(SEM),nitrogen sorption,temperature-programmed reduction by hydrogen(H_2-TPR),ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction(XRD)to obtain the information about the structure and property of the catalysts.H_2-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species,which influences the redox properties of the catalysts.It is found that even a low content of alumina(10 at%)is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components,which ensures the high activity and superior stability of the cobalt-alumina catalysts.

Hydrogen production via catalytic decomposition of NH3 using promoted MgO-supported ruthenium catalysts

Catalytic decomposition of NH3 to high purity hydrogen offers a promising strategy for fuel cells,but presents challenges for high hydrogen yields at comparatively low temperatures due to the lack of efficient catalysts.Here,we report the facile preparation of ultra-fine ruthenium(Ru)species dispersed on MgO,which show excellent activity and high temperature stability for NH3 decomposition reaction.The hydrogen yield of the prepared Ru/MgO catalysts reaches ca.2,092 mmol H2 gRu^-1 min^-1 at 450℃,far exceeding that of the previously reported most reactive Ru・based catalysts and the same chemical composition samples prepared by other approaches.Various characterization techniques containing X-ray absorption fine structure(XAFS),in-situ diffuse reflectance infrared Fourier transform spectroscopy(in-situ DRTFTS)and temperature-programmed reduction/desorption(TPR/TPD)were carried out to explore the structure-function relation of the prepared Ru/MgO catalysts.We found that the Ru species interact strongly with the MgO support,which can efficiently protect the Ru species and MgO support from agglomerating during NH3 decomposition test,maintaining the stability of the catalysts.

Insight into the Role of Isolated Gold Atoms-Ceria Conjunction in Catalyzing the Water-Gas Shift Reaction

As the promising catalysts for the water-gas shift(WGS)reaction,the activity of Au-CeO_(2) composites is susceptible to the aggregation size and electronic state of Au species.Previous reports were extensively focused on the discrepancy between nonmetallic Au and metallic Au nanoparticles,whereas the understanding of the authentic role of the isolated Au atoms was limited.Herein,we investigated the catalytic behavior and structural information over two types of Au/CeO_(2) catalysts,in which the predominant conjunctions were isolated Au1-CeO_(2) and Aun-CeO_(2),respectively.Based on comprehensive characterizations,particularly by in-situ Raman and in-situ DRIFTS,we found that the isolated Au atoms were responsible for enhancing the reducibility of the CeO_(2) matrix.The CO adsorption ability on the isolated Au sites was significantly inferior to clustered Au atoms,especially at relatively high temperatures(>200°C).As a result,the boosted O vacancy on the isolated Au1-CeO_(2) conjunctions could improve the H2O activation ability for the Au-CeO_(2) catalysts and demonstrate a comparable activity to the clustered Aun-CeO_(2) sites.This work might deepen understanding of the catalytic function for the isolated Au1 site within Au/CeO_(2) systems while catalyzing the WGS reaction.