On the plot of yields vs. XCu and XC (Fig. ), an extended maximum limited by brown area can be observed, this are is approximately located between XC values 2.75 and 3.75, and for XCu < Reusability and heterogeneity of Cu@SiO2 composites were studied on the example of the Cu@SiO2-18 and Cu@SiO2-19, which were selected as the most productive composites among other samples in this study. According to XRD data, no copper chloride or copper oxide was included in the Cu@SiO2-18. Cu content in this composite was 5.3 % by weight. The first catalytic cycle was carried out with Cu@SiO2-18 during 3.5 h at reflux. The solid residue of Cu@SiO2-18 after the catalytic experiment was separated by filtration, washed with 15 mL isopropyl alcohol, dried under vacuum (15 Torr) at 45 °C and a small amount of the Cu@SiO2-18 and the reaction mixture after the catalytic experiment were analyzed by AAS to determine the copper leaking. The remaining part of Cu@SiO2-18 was used in the next catalytic cycle and copper content in the solid residue of the composite was analyzed again in the same manner. It was found that copper gradually leached out of the Cu@SiO2-18 after each catalytic cycle, and after the 4th cycle, the copper content in the composite decreased to 2.3%. Copper was found by AAS in all reaction mixtures after each catalytic cycle. The yield of the 5,6,7,8-tetrahydroquinoline-6-carboxylate after the second catalytic cycle decreased from 62% to 39% and then it insignificantly decreased in further catalytic cycles, reaching 26% on the fourth cycle. Very similar tendency was found for Cu@SiO2-19. It should be noted, that for the series of samples, obtained by consequent "washing out" of copper from the same statring material, the yield of the product 3 linearly depended on Cu content in the reaction mixture, implying that all Cu atoms in the composite have similar specific catalytic activity.