van der Wal Lars I, Oenema Jogchum, Smulders Luc C J, Samplonius Nonne J, Nandpersad Karan R, Zečević Jovana, de Jong Krijn P
Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands.
ACS Catal. 2021 Apr 2;11(7):3842-3855. doi: 10.1021/acscatal.1c00211. Epub 2021 Mar 12.
The preparation of zeolite-based bifunctional catalysts with low noble metal loadings while maintaining optimal performance has been studied. We have deposited 0.03 to 1.0 wt % Pt on zeolite H-USY (Si/Al ∼ 30 at./at.) using either platinum(II) tetraammine nitrate (PTA, Pt(NH)(NO)) or hexachloroplatinic(IV) acid (CPA, HPtCl·6HO) and studied the nanoscale Pt loading heterogeneities and global hydroconversion performance of the resulting Pt/Y catalysts. Pt/Y samples prepared with PTA and a global Pt loading as low as 0.3 wt % Pt ( / = 0.08 mol/mol, where n is the number of Pt surface sites and is the number of acid sites) maintained catalytic performance during -heptane ( = 210-350 °C, = 10 bar) as well as -hexadecane ( = 170-280 °C, = 5 bar) hydroisomerization similar to a 1.0 wt % Pt sample. For Pt/Y catalysts prepared with CPA, a loading of 0.3 wt % Pt ( / = 0.08 mol/mol) sufficed for -heptane hydroisomerization, whereas a detrimental effect on -hexadecane hydroisomerization was observed, in particular undesired secondary cracking occurred to a significant extent. The differences between PTA and CPA are explained by differences in Pt loading per zeolite Y crystal (size ∼ 500 nm), shown from extensive transmission electron microscopy energy-dispersive X-ray spectroscopy experiments, whereby / ratios could be determined. From earlier studies, it is known that the Al content per crystal of USY varied tremendously and that PTA preferentially is deposited on crystals with higher Al content due to ion-exchange with zeolite protons. Here, we show that this preferential deposition of PTA on Al-rich crystals led to a more constant value of / ratio from one zeolite crystal to another, which was beneficial for catalytic performance. Use of CPA led to a large variation of Pt loading independent of Al content, giving rise to larger variations of / ratio from crystal to crystal that negatively affected the catalytic performance. This study thus shows the impact of local metal loading variations at the zeolite crystal scale (nanoscale) caused by different interactions of metal precursors with the zeolite, which are essential to design and synthesize optimal catalysts, in particular at low noble metal loadings.
研究了在保持最佳性能的同时制备低贵金属负载量的沸石基双功能催化剂。我们使用硝酸四氨合铂（II）（PTA，Pt(NH)(NO)）或六氯铂（IV）酸（CPA，HPtCl·6HO）在H-USY沸石（Si/Al ∼ 30 at./at.）上负载0.03至1.0 wt%的Pt，并研究了所得Pt/Y催化剂的纳米级Pt负载不均匀性和整体加氢转化性能。用PTA制备的Pt/Y样品，其整体Pt负载量低至0.3 wt% Pt（ / = 0.08 mol/mol，其中n是Pt表面位点的数量， 是酸位点的数量），在庚烷（ = 210 - 350 °C， = 10 bar）以及十六烷（ = 170 - 280 °C， = 5 bar）加氢异构化过程中保持了与1.0 wt% Pt样品相似的催化性能。对于用CPA制备的Pt/Y催化剂，0.3 wt% Pt的负载量（ / = 0.08 mol/mol）足以进行庚烷加氢异构化，然而，观察到对十六烷加氢异构化有不利影响，特别是出现了大量不期望的二次裂化。通过广泛的透射电子显微镜能量色散X射线光谱实验表明，PTA和CPA之间的差异是由每个Y沸石晶体（尺寸 ∼ 500 nm）上的Pt负载差异解释的，由此可以确定 / 比率。从早期研究可知，USY每个晶体中的Al含量变化极大，并且由于与沸质子的离子交换，PTA优先沉积在Al含量较高的晶体上。在这里，我们表明PTA在富Al晶体上的这种优先沉积导致从一个沸石晶体到另一个沸石晶体的 / 比率值更恒定，这有利于催化性能。使用CPA导致Pt负载量的大幅变化，与Al含量无关，从而导致从晶体到晶体的 / 比率有更大的变化，对催化性能产生负面影响。因此，这项研究表明了由金属前驱体与沸石的不同相互作用引起的沸石晶体尺度（纳米尺度）上局部金属负载变化的影响，这对于设计和合成最佳催化剂至关重要，特别是在低贵金属负载量的情况下。
