摘 要
严格的环保法规限定了燃料中硫的含量，要求对含硫燃料油的硫进行去除，目前工业上常用的方法是通过深度加氢脱硫(HDS)的方法降低油品中的硫含量，传统的过渡金属硫化物催化剂，由于其结构和性能方面的原因，在加氢精制的活性和选择性方面存在不足，难以满足要求，开发新型高效的表面性质和催化性能类似于贵金属的过渡金属氮化物催化剂是降低油品中硫含量的一个有效方法。本文选用不同的用浸渍法合成的负载型氧化钨催化剂，用H2-N2为还原氮化气，通过程序升温反应的方法合成出系列负载型氮化钨催化剂。通过BET, XRD, TG-DTA和XPS等现代手段表征了所合成的催化剂，评价了催化剂的加氢脱硫催化性能，考察了不同载体和助剂对氮化钨催化剂性能的影响。本文主要工作和结论如下：
1. 氮化钨催化剂的制备
采用在H2-N2混合气（H2与N2摩尔比为5:1）程序升温还原氮化的方法制备了W2N，W2N/γ-Al2O3，W2N/TiO2-γ-Al2O3和添加助剂Ni、Co、P、V的W2N /TiO2-γ-Al2O3催化剂。
2. 载体和助剂对氮化钨催化剂合成的影响
采用原位差热-热重（TG-DTA）技术，研究负氮化钨催化剂的还原氮化过程。
WO3在650℃于氢氮混合气中经过中间产物WOXNY被还原氮化生成氮化产物W2N。WO3/γ-Al2O3和WO3/TiO2-γ-Al2O3催化剂在氢氮混合气中还原氮化过程均为一步过程，由于活性组分与载体存在较强的相互作用，载体表面上的钨物种比WO3较难于还原氮化。WO3/TiO2-γ-Al2O3催化剂的载体与活性组分之间相互作用要弱于WO3/γ-Al2O3催化剂，因此前者更易于被还原氮化，其还原氮化温度选择为650℃～680℃，后者还原氮化温度选择为650℃～700℃。
Ni、Co、P、V助剂的加入可使WO3/ TiO2-γ-Al2O3催化剂的还原氮化易于进行，加助剂的催化剂的还原氮化温度选择在500～600℃之间。
3. 载体和助剂对氮化钨催化剂物化性质的影响
（1）XRD表征结果表明在实验条件下可以制得W2N/γ-Al2O3和W2N/TiO2-γ-Al2O3催化剂，催化剂活性组分在载体表面上较好的分散。
（2）BET表征结果表明TiO2的加入会使γ-Al2O3比表面积减小，γ-Al2O3和TiO2-γ-Al2O3复合载体负载活性组分后比表面积减小，其氮化态负载型催化剂的比表面积与氧化态的比表面积相比稍有下降；W2N/TiO2-γ-Al2O3催化剂以TiO2含量为6%时比表面积最大；添加助剂Ni、Co、V、P后的W2N/TiO2-γ-Al2O3催化剂的比表面积会减小，其中以添加金属Ni制备的负载型氮化钨催化剂比表面积最大。
（3） NH3-TPD表征结果表明TiO2的加入到γ-Al2O3催中可以提高负载型氮化钨催化剂的酸量，其中以TiO2为6%的W2N/TiO2-γ-Al2O3催化剂的酸量最大；Ni、Co、V、P助剂的加入使得W2N/TiO2-γ-Al2O3催化剂的酸量减小。
（4）XPS表征结果表明，负载型氮化钨表面组成中含有不同价态的金属物种，一定数量的高价态物种，可以认为是钝化后表面上形成的一种氮氧化物。W2N/TiO2-γ-Al2O3催化剂表面的低价态钨物种高于W2N/γ-Al2O3催化剂，证明TiO2-γ-Al2O3载体更有利于稳定低价态W物种，或者说有利于提高活性钨物种数量；Ni助剂的加入使得W2N/TiO2-γ-Al2O3催化剂表面上的低价态钨物种数量明显高于Co、P和V助剂。
4．载体和助剂对氮化钨催化剂的加氢脱硫性能的影响
(1) 以γ-Al2O3和TiO2-γ-Al2O3复合载体负载的氮化钨催化剂的噻吩加氢脱硫活性均高于非负载的W2N， γ-Al2O3中加入TiO2做为载体可以提高负载型氮化钨催化剂的加氢脱硫活性，其中TiO2含量为6%的W2N/TiO2-γ-Al2O3催化剂的噻吩加氢脱硫活性最高。
(2) 助剂Ni、Co、P和V对W2N/TiO2-γ-Al2O3催化剂的噻吩加氢脱硫活性均有促进作用，其中助剂Ni对W2N/TiO2-γ-Al2O3催化剂的噻吩加氢脱硫活性的促进作用更显著，Ni-W2N/TiO2-γ-Al2O3催化剂对工业柴油也显示了良好的加氢脱硫活性。
ABSTRACT
Strict environmental regulation for the amount of sulfur in fuel can be expected to be the driving force for deeper HDS of the more stable sulfur-containing molecules. Hydrotreating catalysts based upon transition metal sulfides can not meet the need of deep HDS because of the structures and properties. Developing transition metal nitride catalysts with high activities，which surface properties and catalytic activities are the same as noble metals, is an effective method to eliminate undesirable sulfur. In this thesis a series of supported nitride catalysts with different supports and promoters were prepared by temperture-programed nitriding of the oxidic catalysts synthesized by impregnation in the mixture gas of N2 and H2. The nitride catalysts were characterized by BET, XRD, TG-DTA and XPS . The catalytic activities of the nitride catalysts were investigated through hydrodesulfurization of thiophene、dibenzothiophene and diesel oil .The effect of different supports and promoters on physicochemical prorerties and catalytic activities of the nitride catalysts were studied and discussed. The main work and conclusions of this thesis are as below:
1. Tungsten nitride catalyst preparation
W2N，W2N/γ-Al2O3，W2N/TiO2-γ-Al2O3 catalysts and Ni(Co,P,V)-W2N /TiO2-γ-Al2O3 catalysts prepared by temperture- programed in the mixture gas of N2 and H2 (H2 and a N2 mole ratio is 5:1) .
2. Influence of the support and promoter on the synthesis of tungsten nitride catalyst .
Nitriding process of tungsten nitride catalyst investigated by TG-DTA technique .WO3 was reduced and nitrided to W2N through intermedium WOXNY in the mixture gas of N2 and H2 at 650 ℃. The nitriding of WO3/γ-Al2O3 and WO3/TiO2-γ-Al2O3 catalyst was a step process. Because the stronger interaction between active component and the support , the tungsten species on the supporter surface were more difficultly nitrided than the WO3 . The interaction of the active W species and the support TiO2-γ-Al2O3 of the WO3/γ-Al2O3 catalyst was stronger than that of the WO3/ TiO2-γ-Al2O3 catalyst . Therefore, the nitriding temperature was 650 ℃ ~ 700 ℃ for WO3/γ-Al2O3 catalyst and 650 ℃ ~ 680 ℃ for WO3/TiO2-γ-Al2O3 catalyst.
Adding Ni, Co, P and V promoter to the WO3/ TiO2-γ-Al2O3 could cause the nitriding process to be easily carried out. Their nitriding temperature was 500 ~ 630 ℃ .
3. The influence of the promoter and support on physico-chemical properties of tungsten nitride catalyst .
(1) The XRD results indicated that W2N/γ-Al2O3 and W2N/TiO2 -γ-Al2O3 catalysts could be prepared under the experimental condition . The active W species were better dispersed on the support surface .
(2) The BET results indicated that TiO2 could cause specific surface area of γ-Al2O3 to be reduced and the specific surface area of the γ-Al2O3 and the TiO2-γ-Al2O3 supported W-based catalysts was smaller than the supports . The specific surface area of the oxidic state catalyst was higher than the nitriding state catalyst. The specific surface area of the WO3/TiO2-γ-Al2O3 catalyst with 6% TiO2 was the lagerest. The promoters could cause specific surface area of the W2N /TiO2-γ-Al2O3 catalyst to be reduced and the Ni-W2N /TiO2-γ-Al2O3 catalyst had the lagerest specific surface area .
(3) The NH3-TPD results indicated that adding TiO2 could increase the acid amount of the supported W2N catalysts and the acid amount of the W2N/TiO2-γ-Al2O3 with 6% TiO2 was the lagerest . Adding Ni, Co, V, P could reduce the acid amount of the W2N/TiO2-γ-Al2O3 catalyst.
(4) The XPS results indicated that the surface of W2N had different valence W species and a certain quantity of high valence W species could be considered as one kind of nitrogen oxide compound formed during passivation. the amount of low valence tungsten on the W2N/TiO2-γ-Al2O3 catalyst surface was higher than that of the W2N/TiO2-γ-Al2O3 catalyst, which proved that the TiO2-γ-Al2O3 support could stabilize low valence tungsten. Adding Ni promoter could increase more low valence tungsten on the W2N/TiO2-γ-Al2O3 catalyst than Co、P and V.
4. The influence of the support and promoter on HDS performance of tungsten nitride catalyst.
(1) The thiophene HDS activity of the W2N/TiO2-γ-Al2O3 and W2N/γ-Al2O3 catalyst was higher than W2N. Adding TiO2 into Al2O3 as support could increase the HDS activity of the supported W2N catalyst and the W2N/TiO2-γ-Al2O3 with 6% TiO2 had the highest thiophene HDS activity.
(2) Promoter Ni, Co, P and V could promote the HDS performance of the W2N/TiO2-γ-Al2O3 catalyst, in which the Ni- W2N/TiO2-γ-Al2O3 catalyst had the highest thiophene HDS activity and a higher HDS activity for the diesel oil.
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