Runsheng Zhai

Crystallization and Si incorporation mechanisms of SAPO-34

In this study of the synthesis of SAPO-34 molecular sieves, XRD, SEM, XRF, IR and NMR techniques were applied to monitor the crystalloid, structure and composition changes of the samples in the whole crystallization process in order to get evidence for the crystallization as well as Si incorporation mechanism of SAPO-34. XRD results revealed that the crystallization contained two stages. In the first 2.5 h (the earlier stage), high up to ∼80% of relative crystallinity could be achieved and the crystal size of SAPO-34 was almost the same as that of any longer time, indicating a fast crystallization feature of the synthesis. In this stage, IR revealed that the formation of SAPO-34 framework structure was accompanied by the diminution of hydroxyls, suggesting that crystal nuclei of SAPO-34 may arise from the structure rearrangement of the initial gel and the condensation of the hydroxyls. NMR results reveal that the template and the ageing period are crucial for the later crystallization of SAPO-34. Preliminary structure units similar to the framework of SAPO-34 have already formed before the crystallization began (0 h and low temperature). Evidence from IR, NMR, and XRF shows that the formation of the SAPO-34 may be a type of gel conversion mechanism, the solution support and the appropriate solution circumstance are two important parameters of the crystallization of SAPO-34. Meanwhile, NMR measurements demonstrated that about 80% of total Si atoms directly take part in the formation of the crystal nuclei as well as in the growth of the crystal grains in the earlier stage ( 2.5 h), the relative content of Si increased slightly with a little decrease of Al and P. The increase of Si(4Al) and the appearance of the Si(3Al), Si(2Al), Si(1Al) and Si(0Al) in this stage suggest that substitution of the Si atoms for the phosphorus and for the phosphorus and aluminum pair takes place in the crystallization. The relationship among structure, acidity and crystallization process is established, which suggests a possibility to improve the acidity and catalytic properties by choosing a optimum crystallization time, thus controlling the number and distribution of Si in the framework of SAPO-34.

Interactions in the Fe/TiO2(110) system

Abstract Fe deposited on TiO2(110) has been studied using AES, LEED, ISS, UPS and HREELS. The deposited Fe overlayer is found to grow in a layer-by-layer mode. Oxygen migrates from the subsurface layers of TiO2(110) to the deposited Fe during the deposition process. The chemical species of the deposited Fe depends on the state of oxidation of TiO2(110) and the amount of Fe deposition. The state of the adsorbed CO in this system is found to depend remarkably on the amount of Fe deposited on the TiO2(110) substrate. CO is found to adsorb weakly on a low Fe coverage system of 0.2 ML Fe/TiO2(110), while it is strongly chemisorbed on a high Fe coverage system of 1.7 ML Fe/TiO2(110). Difference in the CO chemisorption behavior is attributed to the different structural characteristics of these two states of the Fe/TiO2(110) system.

Electrocatalytic properties of Cu-Zr amorphous alloy towards the electrochemical hydrogenation of nitrobenzene

Abstract The Cu–Zr amorphous alloy was studied as an electrocatalyst towards the electrochemical hydrogenation of nitrobenzene. The electrocatalyst was activated by chemical etching in HF solution. Resulted changes in the morphology, chemical composition and crystalline structure of the electrocatalyst surface were characterised by scanning electron microscopy, X-ray diffraction and Auger electron spectroscopy. The electrocatalytic properties of the Cu–Zr amorphous alloy were assessed by voltammetric measurements. Due to the formation and aggregation of Zr residue modified Cu nanocrystals on the surface caused by the selective dissolution of Zr components in the chemical etching, the activated amorphous alloy is an effective electrocatalyst for the electrochemical reduction reaction of nitrobenzene with aniline as the main product. The positive shift of the peak potential and accompanying increase in the value of peak current in voltammograms with increasing Cu content and decreasing Zr content of the alloy surface in the chemical etching are indicative of improved electrocatalytic activity.

Decomposition of NO2 on Pt(110): formation of a new oxygen adsorption state

no2 decomposition on pt(1 1 0) was studied by xps and tds at various temperatures. at room temperature, no, decomposes to adsorbed no and oxygen adatoms on pt(1 1 0). strong repulsive interactions exist between the adsorbed no and the oxygen adatoms. above 450 k, noads desorbs completely from the pt(i 10) surface and only adsorbed oxygen is left on the surface. o-2 thermal desorption spectra results reveal that, comparing with oxygen adsorption on pt(1 1 0), no, exposure above 350 k gives rise to an additional oxygen adsorption state on pt(l 10) that desorbs at a lower temperature. the new oxygen adsorption state has an o1s binding energy of 529.2 ev. the formation of the new oxygen adsorption state may be associated with the local phase transition of the pt(l 10) surface from (i x 2) structure to (1 x 1) structure induced by the noads that is formed from no2 decomposition. () 2002 published by elsevie(c) science b.v.

Investigation of oxygen adsorption on Pd (100) with defects

Pd (100) with mesoscopic defects was prepared, and oxygen adsorption on this surface was studied by photoemission electron microscopy (PEEM). The defect surfaces behaved differently towards oxygen adsorption from the Pd (100) surface. Besides the oxygen species adsorbed on the surface, the formation of surface oxide and subsurface oxygen on different facets, as well as surface restructure, was observed by PEEM during oxygen adsorption.

Interaction of oxygen with silver surface at high temperature

The interaction between oxygen and silver surface at high temperature was investigated by Auger electron spectrometer (AES), ISS, X-ray photoelectron spectra (XPS), thermal desorption spectra (TDS) and high-resolution electron energy loss spectra (HREELS). When dosing oxygen to silver surface at 873 K, a new atomic oxygen species forms on the silver surface. This species of oxygen has very high thermal stability, and the TDS experiment shows no detectable desorption peak appearing below 973 K. The O-1s binding energy of this oxygen species is 529.3 eV and HREELS result gives a peak at 352 cm(-1). All these properties show that this kind of atomic oxygen species is different from those previously found on silver surface

An AES, UPS and HREELS study of the oxidation and reaction of NB(110)

Abstract The oxidation of Nb(110) upon oxygen adsorption has been investigated using AES, UPS and HREELS. For low and medium exposures of oxygen, two new loss features at 720 and ∼950 cm −1 develop, which are assigned to NbO and NbONb stretching vibrations, respectively. When oxygen exposure is high, a broad and strong loss peak at 600–900 cm −1 appears, which is due to bulk-like NbONb stretching vibrations, the changes in the vibrational spectroscopy suggest that, with increasing oxidation of the surface, NbO 4 tetrahedra transform into NbO 6 octahedra. Experiments involving methanol adsorption further confirm these results concerning the process of oxidation.

Preparation and adsorption properties of Mo2N model catalyst

Abstract Mo(100)c(2×2)-N, as a model surface for the real Mo2N catalyst, was prepared. The adsorption of CO and 15NO on this model surface were studied by high-resolution electron energy loss spectroscopy (HREELS). It was found that CO and 15NO not only could be adsorbed on the top of the Mo sites but also could react with surface N sites to form surface NCO and N2O species, respectively. This indicated that both the Mo atoms and N atoms of the surface are all active for CO and 15NO adsorption.

The adsorption and reaction of cyclohexanone on the Pt(111) surface

Abstract The interaction of cyclohexanone with the Pt(111) surface has been investigated by HREELS and TDS. At 160 K, the chemisorption of cyclohexanone induces a “red-shift” of the C O stretch band and a decrease in work function. Heating the sample from 220 to 370 K leads to complete disappearance of the dominant CH 2 rocking band at 720 cm −1 and the C O stretching band at 1650 cm −1 , indicating the dehydrogenation of the entire adlayer to form intermediate species. Strong bands of the dehydrogenated species appear at 860 and 3000 cm −1 which is different from phenoxy on Pt(111). Above ∼ 380K, the dehydrogenated species is decomposed to form hydrocarbon fragments and C O which directly desorbs into the vacuum.

Formation of Periodic Arrays of O Vacancy Clusters on Monolayer FeO Islands Grown on Pt(111)

Abstract The structural evolution of a Pt surface with 0.4 monolayer (ML) subsurface Fe on annealing in 1.1 × 10−7 kPa O2 was studied by scanning tunneling microscopy and X-ray photoelectron spectroscopy. When the annealing temperature was 600 K, only dissociative adsorption of O2 occurred, which induced the local restructuring of surface regions. At 750 K, subsurface Fe atoms segregated onto the surface and were oxidized. When the annealing temperature was increased to 850 K, well defined monolayer FeO islands with periodic arrays of defects were formed. The defects were located at the hexagonal closest packed sites (fcc) of FeO Moire unit cells and were either single oxygen vacancies or multiple oxygen vacancies consisting of six missing O atoms. The formation of periodic defects on monolayer FeO islands may be a way to construct active sites on Pt-Fe model catalysts.