Identification of electron-rich mononuclear Ni atoms on TiO2-A distinguished from Ni particles on TiO2-R in guaiacol hydrodeoxygenation pathways,Catalysis Science & Technology

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Identification of electron-rich mononuclear Ni atoms on TiO2-A distinguished from Ni particles on TiO2-R in guaiacol hydrodeoxygenation pathways
Catalysis Science & Technology ( IF 4.4 ) Pub Date : 2020-10-31 , DOI: 10.1039/d0cy01720e
Xiaoqiang Zhang _{1,

2,

3,

4,

5} , Peifang Yan _{1,

2,

3,

4,

5} , Bin Zhao _{6,

7,

8,

9,

10} , Z. Conrad Zhang _{1,

2,

3,

4,

5}

Affiliation

The electronic and structural differences of anatase TiO₂ (TiO₂-A) and rutile TiO₂ (TiO₂-R) supported Ni catalysts are studied to understand the distinctively different catalytic pathways in guaiacol hydrodeoxygenation over Ni/TiO₂-A and Ni/TiO₂-R catalysts. Temperature programmed reduction profiles of NiO/TiO₂-A and NiO/TiO₂-R reveal two types of metal–support interactions. NiO on TiO₂-R requires much higher temperature to reduce than NiO on TiO₂-A by hydrogen reduction. Surface TiO₂-A is partially reduced together with NiO at low temperature driven by strong interaction between reduced Ni and the reducible TiO₂-A surface. In situ X-ray photoelectron spectroscopy (XPS), high resolution TEM (HRTEM), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy of adsorbed CO reveal two types of reduced Ni species on Ni/TiO₂-A: Ni⁰ particles and atomically dispersed electron-rich Ni^δ− atoms. While Ni⁰ particles are formed only at high Ni loadings, they are fully encapsulated by an overlayer of partially reduced TiO_x, making the surface of Ni particles totally inaccessible to CO and to reactants. The electron-rich Ni^δ− atoms are favorably formed at all Ni loadings on the TiO₂-A surface and show only linearly adsorbed CO in the DRIFT spectra. Electron transfer from Ti and O on the TiO₂-A surface to atomically dispersed Ni is indicated by the observation of dominant electron-rich Ni^δ− species in conjunction with Ti^(4+δ)+ and O^(2−δ)− on Ni/TiO₂-A following H₂ reduction. In contrast, the chemical states of metallic Ni⁰ and Ti⁴⁺ remain unchanged on Ni/TiO₂-R after H₂ reduction. The atomically dispersed Ni^δ− species, formed only on the Ni/TiO₂-A surface, is proposed as the active site responsible for the selective hydrodeoxygenation of guaiacol to phenolics. In contrast, the metallic Ni⁰ particles formed on the Ni/TiO₂-R surface catalyze the typical catalytic hydrogenation, preferentially saturating the aromatic ring.

中文翻译：

愈创木酚加氢脱氧途径中TiO2-A上富电子的单核Ni原子与TiO2-R上的Ni颗粒的区别

研究了锐钛矿型TiO ₂（TiO ₂ -A）和金红石型TiO ₂（TiO ₂ -R）负载的Ni催化剂的电子和结构差异，以了解Ni / TiO ₂ -A和Ni /上的愈创木酚加氢脱氧的不同催化途径。TiO ₂ -R催化剂。NiO / TiO ₂ -A和NiO / TiO ₂ -R的程序升温还原曲线揭示了两种类型的金属-载体相互作用。通过氢还原，TiO ₂ -R上的NiO还原要比TiO ₂ -A上的NiO高得多。表面TiO ₂还原的Ni与可还原的TiO ₂ -A表面之间的强相互作用驱动-A在低温下与NiO一起部分还原。吸附的CO的原位X射线光电子能谱（XPS），高分辨率TEM（HRTEM）和漫反射红外傅里叶变换（DRIFT）光谱显示Ni / TiO ₂ -A上两种还原的Ni种类：Ni ⁰颗粒和原子分散的富电子的Ni ^{δ -}原子。尽管仅在高Ni负载下形成Ni ⁰颗粒，但它们被部分还原的TiO _x覆盖层完全包封，使Ni颗粒的表面完全无法进入CO和反应物。富电子的Ni ^{δ -}良好地形成在上的TiO所有Ni负载原子₂ -A表面并仅显示线性吸附CO的DRIFT光谱。选自Ti在TiO上的电子转移和O ₂ -A表面以原子分散的Ni通过主导镍富电子的观察表明^{δ -}物种结合的Ti ^{（4+ δ）+}和O ^{（2- δ） -}上H ₂还原后的Ni / TiO ₂ -A 。相比之下，金属Ni ⁰和Ti ⁴⁺的化学态H ₂还原后在Ni / TiO ₂ -R上保持不变。的原子分散的Ni ^δ^-物种，仅形成在镍/二氧化钛₂ -A表面，提出了作为负责愈创木酚至酚类选择性加氢脱氧活性位点。相反，在Ni / TiO ₂ -R表面上形成的金属Ni ⁰颗粒催化典型的催化氢化，优先使芳族环饱和。

更新日期：2020-11-13

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