## 2 Experimental Section  
All chemicals were procured from Aldrich, Fluka, and Merck chemical companies and used without any further purification. Field emission scanning electron microscopy (FESEM) was recorded using a Sigma Carl Zeiss instrument. Transmission electron microscopy (TEM) images were acquired images show the homogeneous distribution of spherical Pd NPs immobilized on the HAP with average diameters of \(\sim\)5 nm (Figure 1a-c). The scanning TEM (STEM) images clearly affirm that the Pd NPs were comprised of nano-sized particles with approximately spherical morphology (Figure 1d). Comparison study of the energy-dispersive X-ray spectroscopy (EDX) images of HAP (Figure 2) and HAP-Pd (Figure 3) confirmed the successful preparation of the HAP-Pd, with the grain of the spherical Pd NPs pervading a good combination on the HAP surface. As shown in the EDX spectrum (Figure 3), the presence of Pd authenticated the FESEM analysis for the stabilization of Pd NPs on the HAP. The EDX mapping of the HAP-Pd catalyst provides the qualitative results for the distribution of the existing elements in the prepared catalyst matrix; projected distributions of P, Ca, and Pd within the HAP-Pd catalyst are shown in Figure 4. The compositional map confirms the homogeneous distribution of all of the elements in the HAP-Pd catalyst and clearly ascertains the uniformity of the prepared catalyst. The surface composition of the HAP-Pd catalyst was also confirmed by XPS (Figure 5). The survey spectrum shows the surface binding situation, establishing the presence of C, Ca, O, P, and Pd elements in the synthesized catalyst. Figure 4: Elemental mapping of HAP-Pd catalyst confirming the presence of P, Ca, and Pd elements in the prepared catalyst. Figure 3: (**a**) Low, and (**b**) high magnification FESEM images of HAP-Pd catalyst. (**c**) EDX spectrum of HAP-Pd catalyst. The X-ray diffraction (HRXRD) pattern of the Pd-HAP catalyst is shown in Figure 6. The intense Bragg's peaks are observed at 2\(\theta\) = 25.88, 28.97, 31.77, 32.2, 32.9, 34.05, 35.4, 39.2, 39.8, 42.03, 43.08, 46.7, 48.1, 49.47, 64.08, 77.18, and 78.23 [39]. The positions and relative intensities of these peaks clearly match with literature data from the joint committee on powder diffraction system of HAP crystallite (Ca\({}_{10}\)(PO\({}_{4}\))\({}_{6}\)(OH)\({}_{2}\), JCPDS 09-0432), indicating that the structure of the HAP support has not changed after supporting the Pd nanocatalysts. Five characteristic peaks of Pd appearing at 20 = 40.11, 46.66, 68.12, 82.1, and 86.62. (Pd, JCPDS 46-1043) were observed for the HAP-Pd catalyst. To better elucidate the effect of the mild reduction process on Pd NPs morphology and size on the HAP support in this study, we carried out control experiments using commonly-used reductant, NaBH\({}_{4}\), by adapting previously reported procedures [40]. Although the Pd NPs were formed very rapidly on the HAP support, they instantly aggregated right after addition of NaBH\({}_{4}\). TEM and HRTEM images show that the agglomeration of Pd NPs is unavoidable if they are immobilized using harsh reductant (Figure S1). We examined the possibility of immobilizing Pd NPs uniformly and discretely on another solid support, such as carbon, using the introduced mild procedure, and successfully loaded Pd NPs on carbon material. The TEM images of carbon before and after nanocatalyst loading show that the Pd NPs can be stabilized on carbon using this green protocol (Figure S2). Today, growing attention is being paid to green chemistry in organic synthesis using environmentally-friendly processes. Many scientists have accentuated the significance of the greener methods to synthesize heterogeneous catalysts and chemicals [41]. Aqueous solvent provides an ideal alternative as an ecologically-safe media for particular use in this regard. In this investigation, after a greener synthesis of the HAP-Pd catalyst, we explored the catalytic activity of Pd nanocatalysts for the  
Figure 5: XPS analysis of the HAP-Pd catalyst. The inset shows Pd 3d scan.