Dry Reforming of Propane over γ -Al 2 O 3 and Nickel Foam Supported Novel SrNiO 3 Perovskite Catalyst

: The SrNiO 3 perovskite catalyst was synthesized by the citrate sol-gel method and supported on γ -Al 2 O 3 and Nickel foam, which was used to produce syngas (CO and H 2 ) via dry reforming of propane (DRP). Several techniques characterized the physicochemical properties of the fresh and spent perovskite catalyst. The X-ray diffractograms (XRD) characterization conﬁrmed the formation of the perovskite compound. Before the catalytic activity test, SrNiO 3 perovskite catalyst was reduced in the H 2 atmosphere. Results indicated that the H 2 reduction slightly increased the activity of the SrNiO 3 perovskite catalyst. The catalytic activity was examined for the CO 2 /C 3 H 8 ratio of 3 and reaction temperatures in the range of 550 ◦ C–700 ◦ C. The results from the catalytic study achieved 88% conversion of C 3 H 8 and 66% conversion of CO 2 with SrNiO 3 /NiF at 700 ◦ C. Also, syngas with a maximum concentration of 21 vol.% of CO and 29 vol.% of H 2 was produced from the DRP. The strong basicity of SrNiO 3 perovskite enhanced the CO selectivity, resulting in minimal carbon formation. Post reaction catalyst characterization showed the presence of carbon deposition which could have originated from propane decomposition. ◦ C/min. Hydrogen thermal gas TPR TPD Carry out H 2 adsorption room 30 min 2 mixed rate H 2 gas cut Ar room adsorbed H 2 H 2 desorption linear a rate of 5 ◦ C/min Ar


Introduction
The conventional production of synthesis gas (syngas) by methane steam reforming (1) regularly produces a product with higher H 2 /CO values greater than 3 [1,2]. Recently, the attention has been drawn to the conversion of light hydrocarbons with carbon dioxide into the valuable product (syngas) by catalytic reactions, which is known as dry reforming (2) [3]. The result of a product is with a lower H 2 /CO ratio ≤2. This ratio is more suitable for the synthesis of liquid fuels, and chemicals such as olefins, methanol synthesis and Fisher-Tropsch synthesis [4][5][6][7][8]. Propane is a by-product of natural gas and majorly produced in a variety of petroleum refining operations. Primarily, it readily activates at a lower reaction temperature than methane [9]. (1) However, the steam and dry are an endothermic reaction, which requires high energy to occur reaction. Numerous catalysts have been described for each of the processes mentioned above for various hydrocarbons [10][11][12]. Noble metal catalysts show superior performance regarding the activity and the durability than non-noble metal catalysts. The Ni-based catalysts are attractive and promising due to their high activity, low cost, and abundant availability [13]. It has been widely studied with different support materials such as Al 2 O 3 , SiO 2 , CeO 2 , and SiC, and among them, Al 2 O 3 is the most XRD patterns of the calcined perovskite and reduced perovskite are shown in Figure 1. The sample was calcined at 900 • C and reduced by hydrogen at 700 • C. The fresh catalyst shows the real pattern of SrNiO 3 perovskite state and the somewhat slight secondary peak of NiO also found. As seen in Figure 1, the highest sharp peaks found at 2θ with a value of 32.52 • . It shows the formation of the SrNiO 3 24 • also correspond to SrNiO 3 species. Beside SrNiO 3 phase, some peaks were evolved at 37.04 • , 43.08 • , and 62.76 • , which belong to the NiO crystalline phase. All Ni precursors were not used to form SrNiO 3 . The desired SrNiO 3 catalyst was synthesis successfully, and the diffraction pattern confirms formation of the hexagonal perovskite structure, matched with standard pattern (JCPDS card no: 33-1347) [30]. The post-reduction catalyst clearly shows the diffraction peaks corresponding to Ni 0 and SrO. The peaks found at 2θ values of 44.4 • , 51.8 • , and 76.3 • correspond to metallic Ni and peaks were evolved at 31.4 • , 36.3 • , and 62.2 • correspond to the SrO crystalline phase. Those peaks were matched with the standard patterns (JCPDS card no: 65-2865 and JCPDS card no: , respectively [31,32]. Generally, the high-temperature reduction of perovskites leads to the formation of nanoparticles of B site metal (e.g., Ni) dispersed on the oxide formed by the A site metal (e.g., Sr) [33,34]. The XRD diffraction of γ-Al 2 O 3 and NiF supported catalysts are shown in Figure 1b,c.
The results indicate the existence of SrNiO 3 , NiO, Ni, SrO peaks in both supported catalysts. The peaks were observed at 2θ values of 45.3 • , and 66.7 • belong to the γ-Al 2 O 3 (JCPDS card no: 02-1420) [35] crystalline phase and peaks were found at 2θ values of 44.4 • , 51.8 • , and 76.3 • correspond to metallic Ni [36]. The N2 physisorption isotherm of the SrNiO3 perovskite is shown in Figure 2. The Brunauer-Emmett-Teller (BET) surface area is 3.3 m 2 g −1 , which is agreed with perovskite materials as reported in the literature [34]. The BET surface area of the catalysts with different supports reported in Table  1, the surface area of reduced catalyst was increased in both support materials compared to the fresh catalyst SrNiO3. It implies that the breakdown of the perovskite structure, leading to formation of Ni/SrO, resulted in the generation of porosity to some extent, which also explains the slight enhancement of surface area of this bulk perovskite after reduction. The surface morphology of the SrNiO3 perovskite catalyst is shown in Figure 3. The high-resolution SEM image reveals the porous and flake structure of the material. From low resolution and high-resolution SEM images, it shows the less impact of particle agglomeration due to the citrate sol-gel method [37].  The N 2 physisorption isotherm of the SrNiO 3 perovskite is shown in Figure 2. The Brunauer-Emmett-Teller (BET) surface area is 3.3 m 2 g −1 , which is agreed with perovskite materials as reported in the literature [34]. The BET surface area of the catalysts with different supports reported in Table 1, the surface area of reduced catalyst was increased in both support materials compared to the fresh catalyst SrNiO 3 . It implies that the breakdown of the perovskite structure, leading to formation of Ni/SrO, resulted in the generation of porosity to some extent, which also explains the slight enhancement of surface area of this bulk perovskite after reduction. The surface morphology of the SrNiO 3 perovskite catalyst is shown in Figure 3. The high-resolution SEM image reveals the porous and flake structure of the material. From low resolution and high-resolution SEM images, it shows the less impact of particle agglomeration due to the citrate sol-gel method [37].   Temperature programmed reduction (H2-TPR) analysis was determined by the reduction behavior of the fresh catalyst and reduced catalyst. Figure 4 shows the H2-TPR profile of the fresh catalyst and reduced SrNiO3 perovskite catalyst. The two intense peaks were observed at lower and higher temperatures (600 K and 987 K, respectively) of the SrNiO3 fresh catalyst. The reduced SrNiO3 exhibited one broad peak at higher temperature 1096 K. The fresh calcined SrNiO3 catalyst reduction process occurred by the following steps. The first step at lower temperature 600 K is attributed to Ni 3+ reduction to Ni 2+ and, the second peak at 987 K corresponds to the complete reduction of the perovskite to form Ni 0 (Equation (3)) [27].
The reduced SrNiO3 perovskite shows the single reduction peak at high temperature, which means the complete reduction of SrNiO3 phase to SrO. The perovskite compound's reduction occurred at high temperature, which agreed with the previous report [38]. The reducibility of fresh and reduced SrNiO3 perovskite supported with γ-Al2O3 and nickel foam is presented in Figure 4b. The reduction peaks were observed in the supported catalysts significantly matched with unsupported catalysts. The peaks were evolved at lower region 624 °K, 585 °K, and at higher region 948 °K, 970 °K of γ-Al2O3 and NiF supported catalysts confirmed the reduction properties of fresh SrNiO3 perovskite. Those peaks were shifted to the lower temperature than an unsupported catalyst, which shows the interaction of support. The peak was found at around 1054 °K of both supported catalysts, which matched with the reduced SrNiO3 perovskite. The reducibility of the both supported  Temperature programmed reduction (H2-TPR) analysis was determined by the reduction behavior of the fresh catalyst and reduced catalyst. Figure 4 shows the H2-TPR profile of the fresh catalyst and reduced SrNiO3 perovskite catalyst. The two intense peaks were observed at lower and higher temperatures (600 K and 987 K, respectively) of the SrNiO3 fresh catalyst. The reduced SrNiO3 exhibited one broad peak at higher temperature 1096 K. The fresh calcined SrNiO3 catalyst reduction process occurred by the following steps. The first step at lower temperature 600 K is attributed to Ni 3+ reduction to Ni 2+ and, the second peak at 987 K corresponds to the complete reduction of the perovskite to form Ni 0 (Equation (3)) [27].
The reduced SrNiO3 perovskite shows the single reduction peak at high temperature, which means the complete reduction of SrNiO3 phase to SrO. The perovskite compound's reduction occurred at high temperature, which agreed with the previous report [38]. The reducibility of fresh and reduced SrNiO3 perovskite supported with γ-Al2O3 and nickel foam is presented in Figure 4b. The reduction peaks were observed in the supported catalysts significantly matched with unsupported catalysts. The peaks were evolved at lower region 624 °K, 585 °K, and at higher region 948 °K, 970 °K of γ-Al2O3 and NiF supported catalysts confirmed the reduction properties of fresh SrNiO3 perovskite. Those peaks were shifted to the lower temperature than an unsupported catalyst, which shows the interaction of support. The peak was found at around 1054 °K of both supported catalysts, which matched with the reduced SrNiO3 perovskite. The reducibility of the both supported Temperature programmed reduction (H 2 -TPR) analysis was determined by the reduction behavior of the fresh catalyst and reduced catalyst. Figure 4 shows the H 2 -TPR profile of the fresh catalyst and reduced SrNiO 3 perovskite catalyst. The two intense peaks were observed at lower and higher temperatures (600 K and 987 K, respectively) of the SrNiO 3 fresh catalyst. The reduced SrNiO 3 exhibited one broad peak at higher temperature 1096 K. The fresh calcined SrNiO 3 catalyst reduction process occurred by the following steps. The first step at lower temperature 600 K is attributed to Ni 3+ reduction to Ni 2+ and, the second peak at 987 K corresponds to the complete reduction of the perovskite to form Ni 0 (Equation (3)) [27].
The reduced SrNiO 3 perovskite shows the single reduction peak at high temperature, which means the complete reduction of SrNiO 3 phase to SrO. The perovskite compound's reduction occurred at high temperature, which agreed with the previous report [38]. The reducibility of fresh and reduced SrNiO 3 perovskite supported with γ-Al 2 O 3 and nickel foam is presented in Figure 4b. The reduction peaks were observed in the supported catalysts significantly matched with unsupported catalysts. The peaks were evolved at lower region 624 • K, 585 • K, and at higher region 948 • K, 970 • K of γ-Al 2 O 3 and NiF supported catalysts confirmed the reduction properties of fresh SrNiO 3 perovskite. Those peaks were shifted to the lower temperature than an unsupported catalyst, which shows the interaction of support. The peak was found at around 1054 • K of both supported catalysts, which matched with the reduced SrNiO 3 perovskite. The reducibility of the both supported catalysts showed the metal support interaction enhance the accessibility of active species to the reactant.
catalysts showed the metal support interaction enhance the accessibility of active species to the reactant.  Figure 5 shows the chemisorption characters of SrNiO3 perovskite by H2 temperature programmed desorption method. As seen in Figure 5, the two distinct peaks were observed at 373 °C, and 426 °C. The first peaks attributed to the H2 molecules desorbed from the metal particles, and they represent the outer positioned of Ni atoms in the perovskite lattice [39,40]. The second sharp peak attributed to the H2 dissociated in the subsurface layers of the perovskite lattice. This phenomenon is known as H2 spillover [41][42][43]. It reveals the high energy requires to unbind the H2 molecules and strong enough of chemisorption. From the results, the amount of H2-chemisorbed molecules was estimated under the curve. The H2 consumption amount of the SrNiO3 catalyst was 1.89 × 10 20 −1 .

Catalytic Activity
The activity of perovskite catalysts has been studied in two forms without reduction and reduced with H2 before reaction. The reduced catalysts have shown the significant activity than a fresh catalyst. The reduction process happened to reduce the transition metal phase of the catalyst to a metallic phase, which is located at the active site of the catalyst [44]. It has been reported that reduction enhances the metal dispersion, thereby providing an adequate platform for propane dry reforming reaction to occur. Reduction step has been reported to improve the reactant conversion as  Figure 5 shows the chemisorption characters of SrNiO 3 perovskite by H 2 temperature programmed desorption method. As seen in Figure 5, the two distinct peaks were observed at 373 • C, and 426 • C. The first peaks attributed to the H 2 molecules desorbed from the metal particles, and they represent the outer positioned of Ni atoms in the perovskite lattice [39,40]. The second sharp peak attributed to the H 2 dissociated in the subsurface layers of the perovskite lattice. This phenomenon is known as H 2 spillover [41][42][43]. It reveals the high energy requires to unbind the H 2 molecules and strong enough of chemisorption. From the results, the amount of H 2 -chemisorbed molecules was estimated under the curve. The H 2 consumption amount of the SrNiO 3 catalyst was 1.89 × 10 20 g −1 cat . catalysts showed the metal support interaction enhance the accessibility of active species to the reactant.  Figure 5 shows the chemisorption characters of SrNiO3 perovskite by H2 temperature programmed desorption method. As seen in Figure 5, the two distinct peaks were observed at 373 °C, and 426 °C. The first peaks attributed to the H2 molecules desorbed from the metal particles, and they represent the outer positioned of Ni atoms in the perovskite lattice [39,40]. The second sharp peak attributed to the H2 dissociated in the subsurface layers of the perovskite lattice. This phenomenon is known as H2 spillover [41][42][43]. It reveals the high energy requires to unbind the H2 molecules and strong enough of chemisorption. From the results, the amount of H2-chemisorbed molecules was estimated under the curve. The H2 consumption amount of the SrNiO3 catalyst was 1.89 × 10 20 −1 .

Catalytic Activity
The activity of perovskite catalysts has been studied in two forms without reduction and reduced with H2 before reaction. The reduced catalysts have shown the significant activity than a fresh catalyst. The reduction process happened to reduce the transition metal phase of the catalyst to a metallic phase, which is located at the active site of the catalyst [44]. It has been reported that reduction enhances the metal dispersion, thereby providing an adequate platform for propane dry reforming reaction to occur. Reduction step has been reported to improve the reactant conversion as

Catalytic Activity
The activity of perovskite catalysts has been studied in two forms without reduction and reduced with H 2 before reaction. The reduced catalysts have shown the significant activity than a fresh catalyst. The reduction process happened to reduce the transition metal phase of the catalyst to a metallic phase, which is located at the active site of the catalyst [44]. It has been reported that reduction enhances the metal dispersion, thereby providing an adequate platform for propane dry reforming reaction to occur. Reduction step has been reported to improve the reactant conversion as well as syngas formation [45]. In this experiment, catalytic activity was examined to determine reactants conversion for the reduced and unreduced catalyst with different supports. As seen in Figure 6, the catalytic activity of SrNiO 3 /γ-Al 2 O 3 (F and R) and SrNiO 3 /NiF (F and R) catalysts showed that increases conversion of C 3 H 8 and CO 2 with increasing reaction temperature ranged from 550 • C to 700 • C. In terms of C 3 H 8 conversion, the SrNiO 3 /γ-Al 2 O 3 (R) showed that the higher conversion among all other catalysts. It showed a maximum 94% of C 3 H 8 conversion at 700 • C and minimum 24% conversion at 550 • C, which is higher than the SrNiO 3 /γ-Al 2 O 3 (F) catalyst. The C 3 H 8 conversion of the Ni supported catalysts shows the increasing conversion with increases reaction temperature. The C 3 H 8 conversion of SrNiO 3 /NiF (F and R) catalyst is 81% and 87% at 700 • C, respectively. The unreduced catalysts showed the lower C 3 H 8 conversion with compare to the reduced catalysts. These indicated that in-situ catalyst reduction occurred by H 2 arising from the C 3 H 8 cracking to produce H 2 and carbon [46].
Interestingly, the CO 2 conversion of the SrNiO 3 /NiF (F and R) catalysts showed the significant conversion of CO 2 than the SrNiO 3 /γ-Al 2 O 3 (F and R) catalyst. Among all the catalysts, SrNiO 3 /NiF(R) showed the 69% of CO 2 conversion, which was 13% higher than the SrNiO 3 /γ-Al 2 O 3 (R). It suggested that the SrNiO 3 /NiF(R) leads to the dry reforming reaction even at increasing temperature while the SrNiO 3 /γ-Al 2 O 3 (F and R) has no significant ability to convert CO 2 to CO since it leads the C 3 H 8 cracking reaction and produces more carbon on the surface. well as syngas formation [45]. In this experiment, catalytic activity was examined to determine reactants conversion for the reduced and unreduced catalyst with different supports. As seen in Figure 6, the catalytic activity of SrNiO3/γ-Al2O3 (F and R) and SrNiO3/NiF (F and R) catalysts showed that increases conversion of C3H8 and CO2 with increasing reaction temperature ranged from 550 °C to 700 °C. In terms of C3H8 conversion, the SrNiO3/γ-Al2O3(R) showed that the higher conversion among all other catalysts. It showed a maximum 94% of C3H8 conversion at 700 °C and minimum 24% conversion at 550 °C, which is higher than the SrNiO3/γ-Al2O3(F) catalyst. The C3H8 conversion of the Ni supported catalysts shows the increasing conversion with increases reaction temperature. The C3H8 conversion of SrNiO3/NiF (F and R) catalyst is 81% and 87% at 700 °C, respectively. The unreduced catalysts showed the lower C3H8 conversion with compare to the reduced catalysts. These indicated that in-situ catalyst reduction occurred by H2 arising from the C3H8 cracking to produce H2 and carbon [46]. Interestingly, the CO2 conversion of the SrNiO3/NiF (F and R) catalysts showed the significant conversion of CO2 than the SrNiO3/γ-Al2O3(F and R) catalyst. Among all the catalysts, SrNiO3/NiF(R) showed the 69% of CO2 conversion, which was 13% higher than the SrNiO3/γ-Al2O3(R). It suggested that the SrNiO3/NiF(R) leads to the dry reforming reaction even at increasing temperature while the SrNiO3/γ-Al2O3(F and R) has no significant ability to convert CO2 to CO since it leads the C3H8 cracking reaction and produces more carbon on the surface. The catalytic activity of bare supports is shown in Figure 7. As seen in Figure 7, both bare supports showed low catalytic activities even at 700 °C compared to SrNiO3 loaded catalysts. The conversion of C3H8 of bare γ-Al2O3 shows slightly higher conversion at low temperature than bare NiF and the C3H8 conversion is almost the same (16%) at a higher temperature in both supports. The supports majorly contribute the C3H8 cracking reaction instead of DRP. Moreover, the CO2 conversion of both supports shows the poor activity, which did not reduce to CO. The CO2 conversion of γ-Al2O3 support showed the higher conversion (5%) at low temperatures than C3H8 conversion due to carbon formation from the C3H8 cracking reaction. Hence, the SrNiO3 loaded catalysts show excellent activity compared to the bare supports, which indicates that the supports improve the dispersivity of active catalyst to enhance the interaction of the reactants with active sites.
The outlet concentration of H2 and CO of the catalysts is shown in Figure 8. As seen in Figure 8, the H2 production increases with increasing temperature for all catalyst. The SrNiO3/γ-Al2O3 (F and R) catalysts showed that the higher H2 production compares with SrNiO3/NiF (F and R) catalyst. The maximum H2 and CO production were observed by SrNiO3/γ-Al2O3 (R) is 22% and 20% at 700 °C respectively. It suggested that the γ-Al2O3 supported catalyst primarily enhanced the C3H8 cracking reaction instead of DRP, which leads to the coke generation. Notably, the SrNiO3/NiF (F and R) The catalytic activity of bare supports is shown in Figure 7. As seen in Figure 7, both bare supports showed low catalytic activities even at 700 • C compared to SrNiO 3 loaded catalysts. The conversion of C 3 H 8 of bare γ-Al 2 O 3 shows slightly higher conversion at low temperature than bare NiF and the C 3 H 8 conversion is almost the same (16%) at a higher temperature in both supports. The supports majorly contribute the C 3 H 8 cracking reaction instead of DRP. Moreover, the CO 2 conversion of both supports shows the poor activity, which did not reduce to CO. The CO 2 conversion of γ-Al 2 O 3 support showed the higher conversion (5%) at low temperatures than C 3 H 8 conversion due to carbon formation from the C 3 H 8 cracking reaction. Hence, the SrNiO 3 loaded catalysts show excellent activity compared to the bare supports, which indicates that the supports improve the dispersivity of active catalyst to enhance the interaction of the reactants with active sites.
The outlet concentration of H 2 and CO of the catalysts is shown in Figure 8. As seen in Figure 8, the H 2 production increases with increasing temperature for all catalyst. The SrNiO 3 /γ-Al 2 O 3 (F and R) catalysts showed that the higher H 2 production compares with SrNiO 3 /NiF (F and R) catalyst. The maximum H 2 and CO production were observed by SrNiO 3 /γ-Al 2 O 3 (R) is 22% and 20% at 700 • C respectively. It suggested that the γ-Al 2 O 3 supported catalyst primarily enhanced the C 3 H 8 cracking reaction instead of DRP, which leads to the coke generation. Notably, the SrNiO 3 /NiF (F and R) catalysts have shown 20%, 21%, and 27%, 29% of H 2 and CO production, respectively. The CO 2 conversion always showed lower than the C 3 H 8 conversion, and the H 2 /CO ratio was significantly 0.7 for the SrNiO 3 /NiF (F and R). This observation could be explained by a low amount of coke formation on the surface of the catalyst, and the DRP reaction took place in thermodynamic equilibrium. catalysts have shown 20%, 21%, and 27%, 29% of H2 and CO production, respectively. The CO2 conversion always showed lower than the C3H8 conversion, and the H2/CO ratio was significantly 0.7 for the SrNiO3/NiF (F and R). This observation could be explained by a low amount of coke formation on the surface of the catalyst, and the DRP reaction took place in thermodynamic equilibrium.  As shown in Figure 9, we could compare the SrNiO3 activity in two different supports materials at the isothermal condition. From the results, the NiF foam-supported catalyst showed superior catalytic activity. It could be active in two forms, and the results were almost the same. These suggested that the NiF could be facilitated the significant interaction of the catalytic surface and efficiently enhance the syngas production, which closes to the stoichiometric reaction. As a result of Figure 9, the SrNiO3/NiF(R) revealed the significant conversion of C3H8 and CO2 among all. Regarding CO and H2 selectivity were 96% and 64%, respectively. Moreover, the H2/CO ratio of the catalyst revealed that reaction mechanism, the SrNiO3/γ-Al2O3(F and R) catalysts showed higher values 1.8 and 1.0, respectively, which suggested that the CO selectivity was less than the H2 selectivity. The CO2 conversion was lower than C3H8 conversion due to the additional CO2 produced by water gas shift reaction (WGSR) (Equation (4)). The WGSR was confirmed by the value of H2/CO ratio higher than 1 [34]. The CO selectivity severely affected due to the predominantly produced CO molecules could react with H2O to produce CO2 and H2. Notably, the SrNiO3/NiF (F and R) catalysts have shown the significant conversion of C3H8, CO2 and higher selectivity of CO than the selectivity of H2. The H2/CO ratio is 0.7, which closes to the stoichiometric reaction value of DRP (Equation (2)). catalysts have shown 20%, 21%, and 27%, 29% of H2 and CO production, respectively. The CO2 conversion always showed lower than the C3H8 conversion, and the H2/CO ratio was significantly 0.7 for the SrNiO3/NiF (F and R). This observation could be explained by a low amount of coke formation on the surface of the catalyst, and the DRP reaction took place in thermodynamic equilibrium.  As shown in Figure 9, we could compare the SrNiO3 activity in two different supports materials at the isothermal condition. From the results, the NiF foam-supported catalyst showed superior catalytic activity. It could be active in two forms, and the results were almost the same. These suggested that the NiF could be facilitated the significant interaction of the catalytic surface and efficiently enhance the syngas production, which closes to the stoichiometric reaction. As a result of Figure 9, the SrNiO3/NiF(R) revealed the significant conversion of C3H8 and CO2 among all. Regarding CO and H2 selectivity were 96% and 64%, respectively. Moreover, the H2/CO ratio of the catalyst revealed that reaction mechanism, the SrNiO3/γ-Al2O3(F and R) catalysts showed higher values 1.8 and 1.0, respectively, which suggested that the CO selectivity was less than the H2 selectivity. The CO2 conversion was lower than C3H8 conversion due to the additional CO2 produced by water gas shift reaction (WGSR) (Equation (4)). The WGSR was confirmed by the value of H2/CO ratio higher than 1 [34]. The CO selectivity severely affected due to the predominantly produced CO molecules could react with H2O to produce CO2 and H2. Notably, the SrNiO3/NiF (F and R) catalysts have shown the significant conversion of C3H8, CO2 and higher selectivity of CO than the selectivity of H2. The H2/CO ratio is 0.7, which closes to the stoichiometric reaction value of DRP (Equation (2)). As shown in Figure 9, we could compare the SrNiO 3 activity in two different supports materials at the isothermal condition. From the results, the NiF foam-supported catalyst showed superior catalytic activity. It could be active in two forms, and the results were almost the same. These suggested that the NiF could be facilitated the significant interaction of the catalytic surface and efficiently enhance the syngas production, which closes to the stoichiometric reaction. As a result of Figure 9, the SrNiO 3 /NiF(R) revealed the significant conversion of C 3 H 8 and CO 2 among all. Regarding CO and H 2 selectivity were 96% and 64%, respectively. Moreover, the H 2 /CO ratio of the catalyst revealed that reaction mechanism, the SrNiO 3 /γ-Al 2 O 3 (F and R) catalysts showed higher values 1.8 and 1.0, respectively, which suggested that the CO selectivity was less than the H 2 selectivity. The CO 2 conversion was lower than C 3 H 8 conversion due to the additional CO 2 produced by water gas shift reaction (WGSR) (Equation (4)). The WGSR was confirmed by the value of H 2 /CO ratio higher than 1 [34]. The CO selectivity severely affected due to the predominantly produced CO molecules could react with H 2 O to produce CO 2 and H 2 . Notably, the SrNiO 3 /NiF (F and R) catalysts have shown the significant conversion of C 3 H 8 , CO 2 and higher selectivity of CO than the selectivity of H 2 . The H 2 /CO ratio is 0.7, which closes to the stoichiometric reaction value of DRP (Equation (2)). These indicated that the NiF supported catalysts performed excellently in terms of activity, which aid the DRP reaction and also significantly favor the side reaction reverse water gas shift reaction (Equation (5)). The H 2 /CO ratio would be higher than 1 since this reaction did not occur [47,48].
Catalysts 2019, 9, x FOR PEER REVIEW 8 of 18 These indicated that the NiF supported catalysts performed excellently in terms of activity, which aid the DRP reaction and also significantly favor the side reaction reverse water gas shift reaction (Equation (5)). The H2/CO ratio would be higher than 1 since this reaction did not occur [47,48].
CO + H 2 O → CO 2 + H 2 (4) The catalyst stability of the SrNiO3 perovskite catalysts was examined throughout 50 h at 700 °C shown in Figure 10. It indicated that the SrNiO3/NiF(R) catalyst shows significantly stable catalytic activity during the DRP, among other catalysts. For instance, the SrNiO3/NiF(R) showed no significant conversion loss of C3H8 and CO2 was 85% and 66% from the begin 87% and 69%, respectively, after 50 h of the DRP. The significant activity and long-term stability of SrNiO3/NiF(R) are exhibited for its high thermal stability, high dispersion, and gas permeability of support [30]. In notably, the unreduced SrNiO3 perovskite catalyst showed a gradual decrease the catalytic activity even in two support materials for the period. The conversion of C3H8 and CO2 over the SrNiO3/γ-Al2O3(F) was 87% and 53% until 2 h of the reaction, which gradually decreased to 82% and 48%, respectively, after 50 h due to the amphoteric property of γ-Al2O3.  The catalyst stability of the SrNiO 3 perovskite catalysts was examined throughout 50 h at 700 • C shown in Figure 10. It indicated that the SrNiO 3 /NiF(R) catalyst shows significantly stable catalytic activity during the DRP, among other catalysts. For instance, the SrNiO 3 /NiF(R) showed no significant conversion loss of C 3 H 8 and CO 2 was 85% and 66% from the begin 87% and 69%, respectively, after 50 h of the DRP. The significant activity and long-term stability of SrNiO 3 /NiF(R) are exhibited for its high thermal stability, high dispersion, and gas permeability of support [30]. In notably, the unreduced SrNiO 3 perovskite catalyst showed a gradual decrease the catalytic activity even in two support materials for the period. The conversion of C 3 H 8 and CO 2 over the SrNiO 3 /γ-Al 2 O 3 (F) was 87% and 53% until 2 h of the reaction, which gradually decreased to 82% and 48%, respectively, after 50 h due to the amphoteric property of γ-Al 2 O 3 . These indicated that the NiF supported catalysts performed excellently in terms of activity, which aid the DRP reaction and also significantly favor the side reaction reverse water gas shift reaction (Equation (5)). The H2/CO ratio would be higher than 1 since this reaction did not occur [47,48].
CO + H 2 O → CO 2 + H 2 (4) The catalyst stability of the SrNiO3 perovskite catalysts was examined throughout 50 h at 700 °C shown in Figure 10. It indicated that the SrNiO3/NiF(R) catalyst shows significantly stable catalytic activity during the DRP, among other catalysts. For instance, the SrNiO3/NiF(R) showed no significant conversion loss of C3H8 and CO2 was 85% and 66% from the begin 87% and 69%, respectively, after 50 h of the DRP. The significant activity and long-term stability of SrNiO3/NiF(R) are exhibited for its high thermal stability, high dispersion, and gas permeability of support [30]. In notably, the unreduced SrNiO3 perovskite catalyst showed a gradual decrease the catalytic activity even in two support materials for the period. The conversion of C3H8 and CO2 over the SrNiO3/γ-Al2O3(F) was 87% and 53% until 2 h of the reaction, which gradually decreased to 82% and 48%, respectively, after 50 h due to the amphoteric property of γ-Al2O3.   The catalytic stability results are shown in Table 2, the conversion of C 3 H 8 , CO 2 and the H 2 /CO ratio in the steady state at 700 • C after 50 h. The C 3 H 8 and CO 2 conversion over SrNiO 3 /NiF(R) were superior to other catalysts. Besides, the H 2 /CO ratio was 0.7 for SrNiO 3 /NiF(R) and (F), which is closed to the stoichiometric value of DRP. Moreover, the results claimed that the higher selectivity of nickel foam-supported catalysts resist the carbon formation compared to SrNiO 3 /γ-Al 2 O 3 (F) and (R). According to the results, The SrNiO 3 perovskite catalyst is a basic oxide. Due to its strong basicity, low surface area, and supported by NiF, CO 2 might interact actively with basic sites favoring the formation of carbonates to coverts CO, which minimize the carbon formation during DRP. Several authors [49][50][51] found that the highly basic catalysts like lanthanum oxide and SmCoO 3 are almost present in the carbonate phase on the catalyst surface after reforming reaction. These prevent the sintering of particles and extraction of particles from the surface of carbon filaments during the reaction.
The performance of the dry reforming of methane and propane over the perovskite-type catalysts were compared with the reported results, and the data are presented in Table 3. Strontium substituted perovskite catalyst were performed good catalytic conversion in dry reforming reaction and the H 2 /CO ratio of all the catalysts was less than the 1, which lower than the stoichiometry value of reforming reaction. The comparison suggested the excellent catalytic activity of SrNiO 3 supported catalysts compared to the reported materials.

Catalytic Characterization of Spent Catalyst
The post characterization of catalyst was examined by several techniques such as FE-SEM, Raman, temperature-programmed oxidation (TPO), and XRD to understand the catalyst after DRP at elevated temperature. Figure 11 showed the FE-SEM of all examined catalysts after DRP over time on stream (TOS) 50 h at 1µm magnification. As seen in Figure 11, the morphology of carbon formation on the catalyst was observed whisker/filament form. It is agreed with many previous reports because most of Ni present catalysts are the response to the carbon growth like tubular at high temperature [56,57]. Catalysts 2019, 9, x FOR PEER REVIEW 10 of 18 As shown in Figure 11, the SrNiO3/NiF (R) catalyst showed significantly low carbon on the surface among others, and the form of carbon also was a filament in nature. Figure 12 exhibited the carbon species of the all catalysts after DRP by Raman spectra. From the results, the carbon species were majorly in the form of graphitic. Three active peaks were observed in all catalysts. The first peak at 1337-1342 cm -1 belongs to the D-band of Raman active mode of C-C bond stretching. The second peak at 1572-1580 cm -1 corresponds to the G-band, which attributed to graphitized carbon form and also the third peak at 2678-2691 cm -1 is attributed to the 2D-band of carbon nanotubes or filaments. The intensity of D-band (ID) and intensity of G-band (IG) could explain the graphitic disorder [58,59]. In this case of SrNiO3/γ-Al2O3(F and R) catalyst, the ID was always higher than the IG, which indicates deposited carbon could be in the form of graphite. The SrNiO3/NiF (F and R) catalyst showed that the different trend of ID and IG was almost same, which suggested the existence of crystalline graphite [60].
TPO studies were done to understand the carbon species formation during DRP and its shown in Figure 13. The three primary types of carbon occurred on the surface of the catalyst after DRP. These types were distinguished by oxidation temperature of solid carbon with O2. These are polymeric amorphous films or filaments (Cβ) at 523-773 K, the vermicular carbon filaments/fibers/tubes (Cν) at 573-1273 K and the crystalline graphite (CC) at 773-823 K [61][62][63]. As shown in Figure 11, the SrNiO 3 /NiF (R) catalyst showed significantly low carbon on the surface among others, and the form of carbon also was a filament in nature. Figure 12 exhibited the carbon species of the all catalysts after DRP by Raman spectra. From the results, the carbon species were majorly in the form of graphitic. Three active peaks were observed in all catalysts. The first peak at 1337-1342 cm −1 belongs to the D-band of Raman active mode of C-C bond stretching. The second peak at 1572-1580 cm −1 corresponds to the G-band, which attributed to graphitized carbon form and also the third peak at 2678-2691 cm −1 is attributed to the 2D-band of carbon nanotubes or filaments. The intensity of D-band (ID) and intensity of G-band (IG) could explain the graphitic disorder [58,59]. In this case of SrNiO 3 /γ-Al 2 O 3 (F and R) catalyst, the ID was always higher than the IG, which indicates deposited carbon could be in the form of graphite. The SrNiO 3 /NiF (F and R) catalyst showed that the different trend of ID and IG was almost same, which suggested the existence of crystalline graphite [60].
TPO studies were done to understand the carbon species formation during DRP and its shown in Figure 13. The three primary types of carbon occurred on the surface of the catalyst after DRP. These types were distinguished by oxidation temperature of solid carbon with O 2 . These are polymeric amorphous films or filaments (C β ) at 523-773 K, the vermicular carbon filaments/fibers/tubes (C ν ) at 573-1273 K and the crystalline graphite (C C ) at 773-823 K [61][62][63]. The results of the TPO profile, the reduced catalysts showed the three kinds of Cβ, CC, and Cν on the surface, interestingly the both of reduced catalysts have vermicular carbon filaments. The unreduce catalyst showed the polymeric amorphous films or filaments and crystalline graphite majorly [64]. These suggested that all catalyst produce carbon during DRP, even though the fresh catalyst showed a higher amount of carbon than reduced catalyst. The γ-Al2O3 supported catalysts produced more carbon instead of NiF, which suggested that the NiF allows increasing the molecule interaction due to their porous properties.  The results of the TPO profile, the reduced catalysts showed the three kinds of C β , C C , and C ν on the surface, interestingly the both of reduced catalysts have vermicular carbon filaments. The un-reduce catalyst showed the polymeric amorphous films or filaments and crystalline graphite majorly [64]. These suggested that all catalyst produce carbon during DRP, even though the fresh catalyst showed a higher amount of carbon than reduced catalyst. The γ-Al 2 O 3 supported catalysts produced more carbon instead of NiF, which suggested that the NiF allows increasing the molecule interaction due to their porous properties. The results of the TPO profile, the reduced catalysts showed the three kinds of Cβ, CC, and Cν on the surface, interestingly the both of reduced catalysts have vermicular carbon filaments. The unreduce catalyst showed the polymeric amorphous films or filaments and crystalline graphite majorly [64]. These suggested that all catalyst produce carbon during DRP, even though the fresh catalyst showed a higher amount of carbon than reduced catalyst. The γ-Al2O3 supported catalysts produced more carbon instead of NiF, which suggested that the NiF allows increasing the molecule interaction due to their porous properties.  XRD analysis of the used catalysts was examined after DRP stability test is shown in Figure 14.
The patterns show most of the diffraction peaks were matched with the fresh catalysts patterns (Figure 1b,c). The patterns show the new three peaks at 25.8 • , 46.5 • , and 49.9 • were identified in all catalysts, which corresponds to the SrCO 3 phase (JCPDS card no. 01-0556) [65]. Sutthiumporn et al. [56] reported that the Sr-doped La 2 O 3 catalyst produces bidentate carbonate during the DRM reaction, which majorly reduces the carbon formation by the interaction of CO 2 . The peak at a 2θ value of 25.8 • corresponds to the carbon species of all catalysts, which overlapped with SrCO 3 peak. The reduced catalysts show the high intense peak of SrCO 3 due to SrO reacts with CO 2 to form SrCO 3 [66]. This result confirmed that the higher CO 2 conversion of reduced catalysts than unreduced catalysts.
Catalysts 2019, 9, x FOR PEER REVIEW 12 of 18 XRD analysis of the used catalysts was examined after DRP stability test is shown in Figure 14. The patterns show most of the diffraction peaks were matched with the fresh catalysts patterns (Figure 1b,c). The patterns show the new three peaks at 25.8°, 46.5°, and 49.9° were identified in all catalysts, which corresponds to the SrCO3 phase (JCPDS card no. 01-0556) [65]. Sutthiumporn et al., [56] reported that the Sr-doped La2O3 catalyst produces bidentate carbonate during the DRM reaction, which majorly reduces the carbon formation by the interaction of CO2. The peak at a 2θ value of 25.8° corresponds to the carbon species of all catalysts, which overlapped with SrCO3 peak. The reduced catalysts show the high intense peak of SrCO3 due to SrO reacts with CO2 to form SrCO3 [66]. This result confirmed that the higher CO2 conversion of reduced catalysts than unreduced catalysts.

Synthesis of SrNiO3 Compound
SrNiO3 based perovskite catalyst was prepared by the citric acid sol-gel method. In a typical preparation method, the precursor of 0.02 M of Sr(NO3)2, and Ni(NO3)2·6H2O was dissolved in DI water in two separate beakers. These two solutions were mixed until to get a clear solution. Citric acid (0.06 m) in water was added by dropwise in the above nitrate solution to ensure miscibility. The solution was kept at 80 °C hot plate and stirred gently with Teflon-coated magnetic stir bar until the solution becomes viscous liquid. The resulting solution was kept at 110 °C for 12 h to dried off the excess of water. The dried powder was treated at 450 °C for 5 h to allow combustion reaction the resulting product was foamy. The final powder was ground well then calcined at 900 °C for ten hours, resulting in the synthesis of SrNiO3 perovskite compound.

Preparation of Catalyst
The 10 wt.% of catalyst was prepared with different support materials (γ-Al2O3 and NiF) as follow procedure. In order to remove undesired materials on the surface of support materials, both supports were pretreated to remove the moisture in γ-Al2O3 and to remove oxide layers on NiF. The

Synthesis of SrNiO 3 Compound
SrNiO 3 based perovskite catalyst was prepared by the citric acid sol-gel method. In a typical preparation method, the precursor of 0.02 M of Sr(NO 3 ) 2 , and Ni(NO 3 ) 2 ·6H 2 O was dissolved in DI water in two separate beakers. These two solutions were mixed until to get a clear solution. Citric acid (0.06 m) in water was added by dropwise in the above nitrate solution to ensure miscibility. The solution was kept at 80 • C hot plate and stirred gently with Teflon-coated magnetic stir bar until the solution becomes viscous liquid. The resulting solution was kept at 110 • C for 12 h to dried off the excess of water. The dried powder was treated at 450 • C for 5 h to allow combustion reaction the resulting product was foamy. The final powder was ground well then calcined at 900 • C for ten hours, resulting in the synthesis of SrNiO 3 perovskite compound.

Preparation of Catalyst
The 10 wt.% of catalyst was prepared with different support materials (γ-Al 2 O 3 and NiF) as follow procedure. In order to remove undesired materials on the surface of support materials, both supports were pretreated to remove the moisture in γ-Al 2 O 3 and to remove oxide layers on NiF. The γ-Al 2 O 3 pellets were washed several times with DI water to swipe out of loss bound particles on the surface final rinse with ethanol and then kept at 150 • C for 2 h to remove moistures. The purchased NiF was soaked in 1.0 M HCl solution for 30 min to remove the surface oxide layer and then washed several times with DI water to remove excess of acid and finally rinsed with ethanol and kept 110 • C for 1 h. The 16.0 mm diameter disc of pretreated NiF was cut by hole puncher to attain a disc shape. The desired amount (0.2 gm) of SrNiO 3 was ground with polyvinylidene difluoride (catalyst:PVDF ratio: 95:5) using N-methyl pyrrolidone (NMP) as a solvent to form a slurry. The 1.8 gm of the NiF discs (16 mm; OD) support was then coated with the prepared slurry, and the coated support was allowed to dry in an air oven at 85 • C for 12 h. The pretreated γ-Al 2 O 3 pellets were ground well and made a fine powder, the 1.8 gm of fine γ-Al 2 O 3 powder was mixed with 0.2 gm of SrNiO 3 powder to ensure the blending between γ-Al 2 O 3 and SrNiO 3 . A hydraulic press was used to prepare the pressured pellet, and the pellet was broken down into a small size by manually and sieved with 2 mm of mesh to remove the fine powder.

Material Characterization
X-ray diffractograms (XRD) were recorded an X-ray diffractometer (D/MAX 2200H, Bede 200, Rigaku Instruments C, Tokyo, Japan) with a horizontal goniometer performed by a fine focus copper X-ray tube (40 kV, 40 mA). BET specific surface area was measured by an Autosorb-1-MP instrument (Boynton Beach, FL, USA) at liquid nitrogen temperature. Prior to the analysis, the sample was degassed at 150 • C for 3 h, and the BET multi-point method was applied to estimate the surface area. The surface morphology of the synthesized materials was analyzed by Field-emission scanning electron microscopy (FE-SEM, JSM-6700F, JEOL, Tokyo, Japan). The Raman spectroscopy was evaluated on the samples using Raman HR Evolution Raman Spectrometer (LabRAM Horiba, Longjumeau, France) used at Ar + ion laser operating at 10 mW and a wavelength of 514 nm. Temperature-programmed desorption/reduction (TPD/TPR) experiments were carried out on the gas-chromatography (DS science, DS-6500, Gyeonggi-Do, South Korea) equipped with TCD detector. In case of TPR, the 100 mg of the catalyst sample was loaded in a U-shaped quartz tube and placed on the quartz wool. The temperature of the sample was measured using a thermocouple fixed with quartz tube near the sample. The sample was degassed at 250 • C for 30 min in a flow of Ar (45 mL/min) and to remove the moisture and other adsorbed gases from surface and pores of the sample and then the reactor cooled down to room temperature. The hydrogen was measured with the ramping of the sample temperature to 900 • C with a heating rate of 5 • C/min. Hydrogen consumption was measured by the difference in the thermal conductivity of the gas mixture., Aforementioned in TPR analysis until the degassed was same as the TPD analysis. Carry out H 2 adsorption at room temperature for 30 min by passing 5%H 2 /Ar mixed gas with a flow rate of 50 mL/min. H 2 gas cut off and purge with pure Ar (45 mL/min) at room temperature for 30 min to remove physically adsorbed H 2 . The H 2 desorption signal (as a function of time) was recorded by using a GC-TCD with a linear temperature increase from 25 • C to 800 • C with a heating rate of 5 • C/min under Ar flow (45 mL/min). The amount of desorped H 2 (mol) was measured the area under the curve. The following equation was used to calculate the amount of chemisorped H 2 .
Area(mol) = t 0 [H 2 ]Q total dt (6) where [H 2 ] is a concentration of H 2 in mol/L and Q total is total flow rate L/min. Temperature-programmed oxidation (TPO) experiments of spent catalyst were carried out on the Fourier transform infrared spectroscopy (FTIR) (FTIR-7600 spectrometer, Lambda, Edwardstown, Australia) to understand the nature of carbon species. The 100 mg of spent catalyst was placed in a U-shaped quartz tube and flush with 50 mL/min of N 2 at 250 • C for 30 min prior to remove surface oxygen and to attain inert atmosphere and reactor cool down to room temperature with continues flow of N 2 gas. The 10%O 2 /N 2 (50 mL/min) of oxidant gas feed was changed over, and outlet of gas (CO 2 ) was monitor through online FTIR at a ramped temperature from 25 • C to 900 • C at the rate of 5 • C/min.

Catalytic Activity and Selectivity
The catalytic activity of prepared catalysts was measured in fixed-bed quartz reactor (16 mm ID and 600 mm length). A 2.0 g of the catalyst was placed in the reactor between a sandwich of quartz wool. A tubular furnace has maintained the reaction temperature of the catalyst with an external temperature controller equipped with a K-type thermocouple. The reaction temperature of the catalyst was measured by a K-type thermocouple which fixed on it. The ratio of feed gases of carbon dioxide (CO 2 ) and propane (C 3 H 8 ) (CPR) was 3, the total composition of feed gases are C 3 H 8 :CO 2 :Ar in percentage (10:30:60) and controlled by a mass flow controller (MFC-500, Atovac Co., Yongin, Korea). The total flow rate of the reactant gas is 200 mL/min for all catalytic studies. The concentration of C 3 H 8 and CO 2 were measured by online gas chromatography (GC-Micro-GCCP-4900, 10m PPQ column, Palo Alto, CA, USA) and the concentration of H 2 and CO were measured by GC (DS-Science, 20m-HayeSep-Q column, Gyeonggi-Do, South Korea) equipped with a thermal conductive detector (TCD). The catalytic activity of all catalysts was examined at every 50 • C interval of the temperatures from 550 • C to 700 • C. The conversion of reactants (X A ) and selectivity (S) of various products were calculated by the following equations [67].  (10) where, X A is the conversion of C 3 H 8 and CO 2 , C A0 , and C A are inlet and outlet concentration of reactants C 3 H 8 and CO 2 , respectively, F in and F out are inlet and outlet flow rates (mL/min

Conclusions
SrNiO 3 perovskite catalyst successfully synthesized by the citrate sol-gel method and used as a catalyst with γ-Al 2 O 3 and NiF supports for the first time in propane dry reforming and found to have propane and CO 2 activity for syngas production efficiently. The effect of reduced SrNiO 3 perovskite catalyst on DRP has been investigated. For comparison study, the reduced and unreduced SrNiO 3 catalysts showed significant improvement in conversion of C 3 H 8 and CO 2 . The SrNiO 3 /NiF(R) showed excellent activity regarding syngas production, the syngas produced with a significant selectivity of H 2 and CO and H 2 /CO ratio was maintained close to the stoichiometric value. These measurements of catalytic activity with two different support materials have significantly affected the production of syngas. The results comprise to support perovskites on porous material like metallic foam and high surface area material like γ-Al 2 O 3 to increase the number of exposed perovskite active sites. The strong basicity of strontium metal with NiF could aid the CO production and reduce carbon formation. The finding of this study has presented SrNiO 3 perovskite as a suitable catalyst in the DRP experiment and also could be the replacement of rare earth perovskite in reforming reaction and cost effective with the less health-hazardous catalyst. Funding: This research received no external funding.