**3. Conclusions**

The ionic lamellar coordination polymer based on a flexible triphosphonic acid linker, [Gd(H4nmp)(H2O)2]Cl2 H2O (H6nmp stands for fornitrilo(trimethylphosphonic) acid) presented a high catalytic efficiency to oxidize the most refractory sulfur and nitrogen compounds present in real diesel (mainly dibenzothiophene derivative, indole, and quinolone). The different methods followed for its preparation (microwave, one-pot, hydrothermal) originated some morphological differences, as the size and shape of obtained particles; however, this did not influence its catalytic performance. Using the model diesel/H2O2/[BMIM]PF6 system, complete desulfurization and denitrogenation were achieved after 2 h of reaction using sulfur or nitrogen model diesel, respectively. The ionic liquid [BMIM]PF6 was the extraction solvent selected since its efficiency was higher than MeCN and other more hydrophilic ionic liquids. When the single model diesel was replaced by the multicomponent S/N model diesel, the desulfurization efficiency decreases from 100% to 88% after 2 h, while the denitrogenation effectivity was maintained. The initial extraction (before oxidant addition) for sulfur and nitrogen was maintained when single model diesels were replaced by the multicomponent diesel. However, the extraction of nitrogen compounds is higher (86%) than the sulfur compounds (36%), what contribute largely for the higher efficiency of denitrogenation process. The recycle capacity of the lamellar catalyst was studied for consecutive desulfurization processes and the catalytic efficiency was maintained between cycles. This result indicates that [Gd(H4nmp)(H2O)2]Cl2 H2O is a stable catalyst, although some structural adjustment occurred to form the active heterogeneous catalyst. An improvement in the reuse capacity of the diesel/H2O2/[BMIM]PF6 system need to be performed in the near future, since the desulfurization process catalyzed by the lamellar material loss efficiency in consecutive ECODS cycles, probably caused by the saturation of the extraction [BMIM]PF6 phase with sulfur and nitrogen compounds.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4344/10/7/731/s1, Figure S1: The representative sulfur and nitrogen compounds used in this work to prepare model diesels. 1-benzothiophene (1-BT), dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), Figure S2: Powder X-ray diffraction and SEM images of [Gd(H4nmp)(H2O)2]Cl·2H2O (1) obtained using different experimental methods (op—one-pot; mw—Microwave Assisted; ht—Hydrothermal), Figure S3: Desulfurization of a multicomponent model diesel (2350 ppm S) catalyzed by layered MOF [Gd(H4nmp)(H2O)2]Cl·2H2O (20 mg), using 0.43 mmol of H2O2 oxidant and different volume of [BMIM]PF6 extraction solvent (1:1 and 1:0.5 model diesel/[BMIM]PF6), at 70 ◦C. The vertical dashed line indicates the instant that oxidative catalytic reaction was started by addition of oxidant, Figure S4: Denitrogenation and desulfurization profile of a model diesel containing approximately 400 ppm N and 2200 ppm of S, catalyzed by layered MOF [Gd(H4nmp)(H2O)2]Cl·2H2O (20 mg), 0.43 mmol of H2O2 oxidant and 1:0.5 model diesel/[BMIM]PF6, at 70 ◦C. The vertical dashed line indicates the instant that oxidative catalytic reaction was started by addition of oxidant, Figure S5: SEM, mapping and EDS spectra of compound [Gd(H4nmp)(H2O)2]Cl·2H2O (1) after catalytic use for one cycle of ECODS, with a P:Gd ratio of 3:1, Figure S6: FT-IR spectra of layered [Gd(H4nmp)(H2O)2]Cl·2H2O before and after catalytic use for one ECODS cycle.

**Author Contributions:** Conceptualization, F.A.A.P and S.S.B.; Data curation, F.M. and R.F.M.; Formal analysis, F.M. and R.F.M.; Funding acquisition, S.S.B.; Investigation, F.M.; Project administration, S.S.B.; Supervision, S.S.B. and F.A.A.P.; Validation, F.A.A.P. and R.F.M.; Visualization, F.M.; Writing—original draft, S.S.B.; Writing—review & editing, F.A.A.P and S.S.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was partly funded through the project REQUIMTE-LAQV (Ref. UID/QUI/50006/2019) and the project GlyGold, PTDC/CTM-CTM/31983/2017, and partially developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, LAQV-REQUIMTE (UIDB/50006/2020) and CQE (UIDB/00100/2020) research units, financed by national funds through the FCT/MCTES (Fundação para a Ciência e a Tecnologia / Ministério da Ciência, Tecnologia e Ensino Superior) and when appropriate co-financed by FEDER (Fundo Europeu de Desenvolvimento Regional) under the PT2020 Partnership Agreement. FCT is also gratefully acknowledged for the Junior Research Position CEECIND/00553/2017 (to RFM).

**Conflicts of Interest:** The authors declare no conflict of interest.
