Controlled site coverage of strong metal–support interaction (SMSI) on Pd NP catalysts
Controlled site coverage of strong metal–support interaction (SMSI) on Pd NP catalysts
复制标题
Pd NP 催化剂上强金属与载体相互作用 (SMSI) 的受控位点覆盖
DOI：
10.1039/d2cy01707e
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发表时间：
2023
影响因子：
5
通讯作者：
Miller, Jeffrey T.
中科院分区：
文献类型：
--
作者：
Breckner, Christian J.;Zhu, Kuixin;Wang, Mingrui;Zhang, Guanghui;Li, Christina W.;Miller, Jeffrey T.
强金属-载体相互作用催化剂已显示出以由于活性位点覆盖而导致的分数率为代价来改进期望的产物选择性。本研究的目的是确定金属纳米颗粒的活性位点覆盖率是否可以控制到比以前报道的SMSI催化剂更低的水平，目的是在保持高选择性的同时提高速率。合成了Ti负载量在0-1.0 wt%之间的2 Pd-XTi/SiO2（2 wt% Pd，X wt% Ti）强金属-载体相互作用（SMSI）催化剂以控制Pd纳米颗粒覆盖率。在450 °C下的煅烧和在550 °C下的还原足以在所有催化剂中形成102 nm尺寸的Pd颗粒。在550 °C的固定还原温度下，将Ti负载量从0.1重量%增加到1.0重量%将表面覆盖率从40%增加到85%。SMSI催化剂的红外光谱相似，具有高分数的线性键合CO，其远高于类似尺寸的Pd纳米颗粒。SMSI覆盖层可以通过在350 °C下氧化和在200 °C下再还原来去除。氧化的催化剂的EXAFS表明，需要金属纳米颗粒的几乎完全氧化来去除SMSI覆盖层。30至300 °C的氧化温度部分氧化了Pd纳米颗粒，随后在200 °C下重新还原部分降低了SMSI覆盖度。通过测量有和没有SMSI覆盖层的丙烯加氢速率来确定表面覆盖率。将还原温度从200 °C增加到550 °C将SMSI覆盖率从0增加到85%，这取决于Ti负载和温度。在550 °C下还原和在350 °C下氧化之后，覆盖率的范围在300 °C下再还原之后用0.1重量% Ti覆盖10%和在550 °C下还原之后用1重量% Ti覆盖85%之间变化。
Strong metal–support interaction catalysts have been shown to improve desired product selectivity at the cost of fractional rates due to active site coverage. The goal of this study was to determine if the active site coverage of metallic nanoparticles could be controlled to lower levels than have been previously reported in SMSI catalysts with the aim of improving the rate while maintaining high selectivity. 2Pd–XTi/SiO2 (2 wt% Pd, X wt% Ti) strong metal–support interaction (SMSI) catalysts with Ti loadings between 0–1.0 wt% were synthesized to control Pd nanoparticle coverage. Calcination at 450 °C and reduction at 550 °C were sufficient for forming ∼2 nm sized Pd particles in all catalysts. Increasing the Ti loading from 0.1 to 1.0 wt% increased the surface coverage from 40 to 85% at a fixed reduction temperature of 550 °C. The IR spectra of the SMSI catalysts were similar with a high fraction of linear bonded CO which was much higher than that of Pd nanoparticles of similar size. The SMSI overlayer could be removed by oxidation at 350 °C and re-reduction at 200 °C. EXAFS of the oxidized catalysts indicates that nearly full oxidation of the metallic nanoparticle was required to remove the SMSI overlayer. Oxidation temperatures from 30 to 300 °C partially oxidized the Pd nanoparticles and subsequent re-reduction at 200 °C partially decreases the SMSI coverage. The fractional surface coverage was determined by measuring the rate of propylene hydrogenation with and without the SMSI overlayer. Increasing the reduction temperature from 200 to 550 °C increased the SMSI coverage from 0 to 85% depending on the Ti loading and temperature. After reduction at 550 °C and oxidation at 350 °C, the range of coverages varied between ∼10% with 0.1 wt% Ti after re-reduction at 300 °C and ∼85% with 1 wt% Ti after reduction at 550 °C.