HDO of Methyl Palmitate over Silica-Supported Ni Phosphides: Insight into Ni/P Effect

Abstract

Two sets of silica-supported nickel phosphide catalysts with a nickel content of about 2.5 and 10 wt % and Ni/P molar ratio 2/1, 1/1 and 1/2 in each set, were prepared by way of a temperature-programmed reduction method using (Ni(CH 3 COO) 2 ) and ((NH 4 ) 2 HPO 4 ) as a precursor. The Ni x P y /SiO 2 catalysts were characterized using chemical analysis N 2 physisorption, XRD, TEM, 31 P MAS NMR. Methyl palmitate hydrodeoxygenation (HDO) was performed in a trickle-bed reactor at 3 MPa and 290 • C with LHSV ranging from 0.3 to 16 h −1 . The Ni/P ratio was found to affect the nickel phosphide phase composition, PO x groups content and catalytic properties in methyl palmitate HDO with the TOF increased along with a decline of Ni/P ratio and a growth of PO x groups' content. Taking into account the possible routes of methyl palmitate conversion (metal-catalyzed hydrogenolysis or acid-catalyzed hydrolysis), we proposed that the enhancement of acid PO x groups' content with the Ni/P ratio decrease provides an enhancement of the rate of methyl palmitate conversion through the acceleration of acid-catalyzed hydrolysis.

Methyl palmitate hydrodeoxygenation over silica‐supported nickel phosphide catalysts in flow reactor: experimental and kinetic study

“…Another alternative are transition metal phosphides (Ni 2 P, Co 2 P, MoP) which are active, stable and do not contain sulfur . Research of nickel phosphide catalysts has been quite active in recent years, Ni 2 P/SiO 2 demonstrating high activity in HDO of aliphatic esters …”

“…As to phosphide catalysts, various paths of ester conversion to intermediate products are considered in the reported schemes . Some authors considered alternatively hydrogenolysis (1) or hydrolysis (2) reactions, while both reactions are considered in a number of works . Also, the reaction of ester to aldehyde (3) is included in some schemes, while reaction of ester to alcohol (4) is not included in any schemes for phosphide catalysts.…”

“…Some authors considered alternatively hydrogenolysis (1) or hydrolysis (2) reactions, while both reactions are considered in a number of works . Also, the reaction of ester to aldehyde (3) is included in some schemes, while reaction of ester to alcohol (4) is not included in any schemes for phosphide catalysts. Transesterification of ester (5) is included in one of the schemes and reaction of ester to C n −1 alkene (6) or to C n −1 alkane (7) is considered in several schemes.…”

“…Decarboxylation or decarbonylation of acid to C n −1 alkene (11) or to C n −1 alkane (12) can be found in several schemes. Aldehyde reactions involving hydrogenation to alcohol (13) and decarbonylation to C n −1 alkene (14) or to C n −1 alkane (15) are often discussed …”

“…Dehydration of alcohol to C n alkene (17) along with the direct transformation of alcohol to C n alkane (18) has been considered by various authors. Hydrogenations of C n −1 alkene (19) and C n alkene (20) are generally accepted final stages . Hexadecanol‐1 and hexadecanol‐2 formation in HDO of MP has been reported but without discussion of this observation …”