Preferential oxidation of CO in excess H_2 over the CeO_2/CuO catalyst: Effect of initial support

Three series of CeO2/CuO samples were prepared by impregnation method and characterized by XRD, N2 adsorption-desorption, temperatureprogrammed reduction （TPR）, XPS and TEM techniques. In comparison with the samples prepared with CuO as initial support, the samples with Cu（OH）2 as initial support have higher reducibilities and smaller relative TPR peak areas, and also larger specific surface areas at calcina- tion temperatures of 400 ℃--600 ℃. As a result, Cu（OH）2 is better than CuO as initial support for preferential oxidation of CO in excess H2 （CO-PROX）. The best catalytic performance was achieved on the sample calcined at 600 ℃ and with an atomic ratio of Ce/Cu at 40%. XPS analyses indicate that more interface linkages Ce-O-Cu could be formed when it was calcined at 600 ℃. And the atomic ratio of Ce/Cu at 40% led to a proper reducibility for the sample as illustrated by the TPR measurements.

Effect of Sb-doping on martensitic transformation and magnetocaloric effect in Mn-rich Mn50Ni40Sn10-Sb( = 1, 2, 3, and 4) alloys

We investigate the influence of Sb-doping on the martensitic transformation and magnetocaloric effect in Mn（50）Ni（40）Sn（10-x）Sbx（x = 1, 2, 3, and 4） alloys. All the prepared samples exhibit a B2-type structure with the space group F m3 m at room temperature. The substitution of Sb increases the valence electron concentration and decreases the unit cell volume. As a result, the magnetostructural transformation shifts rapidly towards higher temperatures as x increases.The changes in magnetic entropy under different magnetic field variations are explored around this transformation. The isothermal magnetization curves exhibit typical metamagnetic behavior, indicating that the magnetostructural transformation can be induced by a magnetic field. The tunable martensitic transformation and magnetic entropy changes suggest that Mn（50）Ni（40）Sn（10-x）Sbx alloys are attractive candidates for applications in solid-state refrigeration.

Magnetostructural transformation and magnetocaloric effect in Mn_(48-x)V_(x)Ni_(42)Sn_(10) ferromagnetic shape memory alloys

In this work,we tuned the magnetostructural transformation and the coupled magnetocaloric properties of Mn_(48-x)V_(x)Ni_(42)Sn_(10)(x=0,1,2,and 3)ferromagnetic shape memory alloys prepared by means of partial replacement of Mn by V.It is observed that the martensitic transformation temperatures decrease with the increase of V content.The shift of the transition temperatures to lower temperatures driven by the applied field,the metamagnetic behavior,and the thermal hysteresis indicates the first-order nature for the magnetostructural transformation.The entropy changes with a magnetic field variation of 0-5 T are 15.2,18.8,and 24.3 J.kg^(-1).K^(-1)for the x=0,1,and 2 samples,respectively.The tunable martensitic transformation temperature,enhanced field driving capacity,and large entropy change suggest that Mn_(48-x)V_(x)Ni_(42)Sn_(10)alloys have a potential for applications in magnetic cooling refrigeration.

Enhanced reversibility of the magnetoelastic transition in(Mn,Fe)2(P,Si)alloys via minimizing the transition-induced elastic strain energy

Magnetocaloric materials undergoing reversible phase transitions are highly desirable for magnetic refrigeration applications.(Mn,Fe)_(2)(P,Si)alloys exhibit a giant magnetocaloric effect accompanied by a magnetoelastic transition,while the noticeable irreversibility causes drastic degradation of the magnetocaloric properties during consecutive cooling cycles.In the present work,we performed a comprehensive study on the magnetoelastic transition of the(Mn,Fe)_(2)(P,Si)alloys by high-resolution transmission electron microscopy,in situ field-and temperature-dependent neutron powder diffraction as well as density functional theory calculations(DFT).We found a generalized relationship between the thermal hysteresis and the transition-induced elastic strain energy for the(Mn,Fe)_(2)(P,Si)family.The thermal hysteresis was greatly reduced from 11 to 1 K by a mere 4 at.%substitution of Fe by Mo in the Mn_(1.15)Fe_(0.80)P_(0.45)Si_(0.55)alloy.This reduction is found to be due to a strong reduction in the transition-induced elastic strain energy.The significantly enhanced reversibility of the magnetoelastic transition leads to a remarkable improvement of the reversible magnetocaloric properties,compared to the parent alloy.Based on the DFT calculations and the neutron diffraction experiments,we also elucidated the underlying mechanism of the tunable transition temperature for the(Mn,Fe)_(2)(P,Si)family,which can essentially be attributed to the strong competition between the covalent bonding and the ferromagnetic exchange coupling.The present work provides not only a new strategy to improve the reversibility of a first-order magnetic transition but also essential insight into the electron-spin-lattice coupling in giant magnetocaloric materials.

Large,low-field and reversible magnetostrictive effect in MnCoSi-based metamagnet at room temperature

TiNiSi-type MnCoSi-based alloys show large magnetostriction during the magnetic-field-induced metamagnetic transition.However,the high critical field required to drive the transition directly hinders their potential applications.In this work,we systematically investigate the tricritical behavior and magnetostrictive effect in substituted MnCoSi alloys.Replacing Si with Sb or In,Co with Fe or Cu,and Mn with Co,which can simultaneously reduce the critical field and the temperature of tricritical point,are explored.Among the substituted MnCoSi alloys,Mn_(0.983)Co_(1.017)Si displays a temperature of a tricritical point of 250 K and a room-temperature critical field of 0.60 T,which is the lowest up to now.Profited from these optimizations,a large reversible magnetostrictive effect under low field is successfully realized at room temperature.In a field of 1 T,the magnetostriction of Mn_(0.983)Co_(1.017)Si alloy is close to 1000 ppm.Besides,a strong relation between critical field and valence electron concentration is revealed in the transition-metal-substituted MnCoSi alloys.Our work greatly enhances the low-field magnetostrictive performance of MnCoSi-based alloys and make them be of interest in potential applications.

Crystallography of the martensitic transformation between Ni_2In-type hexagonal and TiNiSi-type orthorhombic phases

MnMX(M=Co or Ni,X=Si or Ge)alloys,experiencing structural transformation between Ni_(2) In-type hexagonal and TiNiSi-type orthorhombic phases,attract considerable attention due to their potential applications as room-temperature solid refrigerants.Although lots of studies have been carried out on how to tune this transformation and obtain large entropy change in a wide temperature region,the crystallography of this martensitic transformation is still unknown.The biggest obstacle for crystallography investigation is to obtain a bulk sample,in which hexagonal and orthorhombic phases coexist,because the MnMX alloys will fragment into powders after experiencing the transformation.For this reason,we carefully tune the transformation temperature to be slightly below 300 K.In that case,a bulk sample with small amounts of orthorhombic phases distributed in hexagonal matrix is obtained.Most importantly,there are no cracks between the two phases.It facilities us to investigate the microstructure using electron microscope.The obtained results indicate that the orientation relationship between hexagonal and orthorhombic structures is[4223]_(h)//[120]_(o)&(0110)_(h)//(001)_(o) and the habit plane is{2113.26}_(h).WLR theory is also adopted to calculate the habit plane.The calculated result agrees well with the measured one.Our work reveals the crystallography of hexagonal-orthorhombic transformation for the first time and is helpful for understanding the transformation-associated physical effects in MnMX alloys.