Enhancing both selectivity and coking-resistance of a single-atom Pd1/C3N4 catalyst for acetylene hydrogenation

Selective hydrogenation is an important industrial catalytic process in chemical upgrading, where Pd-based catalysts are widely used because of their high hydrogenation activities. However, poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns. In this work, atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride （g-C3N4） using atomic layer deposition. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy （HAADF-STEM） confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle （NP） formation. During selective hydrogenation of acetylene in excess ethylene, the g-C3N4-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/Al2O3 and Pd/SiO2 catalysts. In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C3N4 likely plays an important role in the catalytic performance enhancement. More impressively, the single-atom Pd1/C3N4 catalyst exhibited both higher ethylene selectivity and higher coking resistance. Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.

Preparation of Uniform Ni-B Amorphous Alloy Catalyst on CNTs and its Performance for Acetylene Selective Hydrogenation

Uniform Ni-B amorphous alloys about 14 nm have been prepared on CNTs-A support,named Ni-B/CNTs-A. In comparison with the Ni-B/CNTs amorphous catalyst, Ni-B/CNTs-A showed higher nickel loading, determined by ICP and better catalytic activity and ethylene selectivity in the acetylene hydrogenation reaction.

Investigation of the preparation methodologies of Pd-Cu single atom alloy catalysts for selective hydrogenation of acetylene

Galvanic replacement, co-impregnation and sequential impregnation have been employed to prepare Pd-Cu bimetallic catalysts with less than 1 wt-% Cu and ca. 0.03 wt-% Pd for selective hydrogenation of acetylene in excess ethylene. High angle annular dark field-scanning transmission electron microscopy （HAADF-STEM） and H2 chemisorption results confirmed that Pd-Cu singleatom alloy structures were constructed in all three bimetallic catalysts. Catalytic tests indicated that when the conversion of acetylene was above 99%, the selectivity of ethylene of these three single atom alloy catalysts was still more than 73%. Furthermore, the single atom alloy catalyst prepared by sequential incipient wetness impregnation was found to have the best stability among the three procedures used.

Layered Double Hydroxides Derived ZnO-Al2O3 Supported Pd-Ag Catalysts for Selective Hydrogenation of Acetylene

ZnO-Al2O3 derived from layered double hydroxides （ZnAl-LDH） was successfully applied for dispersion of Pd-Ag bimetallic catalysts for the selective hydrogenation of acetylene to ethylene and the Pd-Ag/ZnO-Al2O3 cata- lyst showed the best catalytic performance among the prepared samples. It was found that the catalyst carrier of ZnO-Al2O3 metal-oxides derived form ZnAl-LDH could significantly suppress the over-hydrogenation of acetylene to obtain the relatively higher selectivity of ethylene. The introduction of Ag restricted efficiently the formation of coke because of the oligomerization reaction, which was further evidenced by thermal gravimetric analysis. The se- lectivity towards ethylene was in the order of Pd-Ag/ZnO-Al2O3〉Pd/ZnO-Al2O3〉Pd-Ag/Al2O3〉Pd/Al2O3 at a high conversion level. As the thermal gravimetric and differential temperature analysis （TG-DTA） revealed, Pd-Ag intermetallic catalyst on the ZnO-Al2O3 support showed less coke formation.

Pd single-atom catalysts derived from strong metal-support interaction for selective hydrogenation of acetylene

Selective hydrogenation of acetylene in excess ethylene is an important reaction in both fundamental study and practical application.Pd-based catalysts with high intrinsic activity are commonly employed,but usually suffer from low selectivity.Pd single-atom catalysts(SACs)usually exhibit outstanding ethylene selectivity due to the weakπ-bonding ethylene adsorption.However,the preparation of high-loading and stable Pd SACs is still confronted with a great challenge.In this work,we report a simple strategy to fabricate Pd SACs by means of reducing conventional supported Pd catalysts at suitable temperatures to selectively encapsulate the co-existed Pd nanoparticles(NPs)/clusters.This is based on our new finding that single atoms only manifest strong metal-support interaction(SMSI)at higher reduction temperature than that of NPs/clusters.The derived Pd SACs(Pd1/CeO2 and Pd1/a-Fe2O3)were applied to acetylene selective hydrogenation,exhibiting much improved ethylene selectivity and high stability.This work offers a promising way to develop stable Pd SACs easily.

TiO_2-modified nano-egg-shell Pd catalyst for selective hydrogenation of acetylene

Pd-based egg-shell nano-catalysts were prepared using porous hollow silica nanoparticles （PHSNs） as support, and the as-prepared catalysts were modified with TiO2 to promote their selectivity for hydro-genation of acetylene. Pd nanoparticles were loaded evenly on PHSNs and TiO2 was loaded on the active Pd particles. The effects of reduction time and temperature and the amount of TiO2 added on catalytic per-formances were investigated by using a fixed-bed micro-reactor. It was found that the catalysts showed better performance when reduced at 300 ℃ than at 500℃, and if reduced for 1 h than 3 h. When the amount of Ti added was 6 times that of Pd, the catalyst showed the highest ethylene selectivity.

A two-dimensional microporous metal–organic framework for highly selective adsorption of carbon dioxide and acetylene

Solvothermal reaction of 3-aminoisonicotinic acid（Haina） and Cu（NO_3）_2·2.5H_2O gave a novel twodimensional（2D） microporous metal–organic framework, [Cu（aina）_2（DMF）]·DMF（1, DMF = N,N-dimethylformamide）. Single-crystal X-ray crystallographic study of compound 1 revealed that Cu（II）ions are linked by ainaàligands forming square grid-like layers, which stack together via multiple hydrogen bonding interactions. The solvent-free framework of 1a displayed considerable porosity（void = 46.5%） with one-dimensional（1D） open channels（4.7 ？ ？ 4.8 ？） functionalized by amino groups.Gas sorption measurements of 1 revealed selective carbon dioxide（CO_2） and acetylene（C_2H_2） adsorption over methane（CH_4） and nitrogen（N_2） at ambient temperature.

石墨烯负载的非贵金属单原子催化剂的乙炔选择性加氢反应研究

在工业上批量生产聚乙烯的过程中去除痕量乙炔杂质的常用方法是沸石吸附或钯基催化剂选择性半氢化乙炔生成乙烯.本文通过密度泛函理论研究了乙炔在缺陷石墨烯负载的单原子催化剂M1/SV-G和M1/DV-G(其中M=Ni,Pd,Pt;SV-G,DV-G分别代表具有单碳缺陷和双碳缺陷的石墨烯)表面上加氢转化为乙烯的反应机理.研究表明,金属单原子及其配位环境均会影响加氢过程的活性和选择性.M1/DV-G催化剂比M1/SV-G具有更好的氢分子解离能力,这是因为M1/DV-G具有较强的乙炔氢化能力.基于计算得到的加氢能垒,Pt1/DV-G和Ni1/DV-G的催化活性明显优于其他催化剂,其中Ni1/DV-G催化剂还具有高的乙炔半加氢选择性.本研究结果为设计以碳材料为载体的、具有高选择性的非贵金属单原子乙炔氢化催化剂提供了理论基础.