Pd‐Ag/α‐Al₂O₃ Catalyst Deactivation in Acetylene Selective Hydrogenation Process

Abstract

The selective hydrogenation of acetylene to ethylene over Pd‐Ag/α‐Al2O3 catalysts prepared by different impregnation/reduction methods was studied. The best catalytic performance was achieved with the sample prepared by sequential impregnation. A kinetic model based on first order in acetylene and 0.5th order in hydrogen for the main reaction and second‐order independent decay law for catalyst deactivation was used to fit the conversion time data and to obtain quantitative assessment of catalyst performances. Fair fits were observed from which the reaction and deactivation rate constants were evaluated. Coke deposition amounts showed a good correlation with catalyst deactivation rate constants, indicating that coke formation should be the main cause of catalyst deactivation.

Highly Dispersed PdNPs/α-Al2O3 Catalyst for the Selective Hydrogenation of Acetylene Prepared with Monodispersed Pd Nanoparticles

“…For supported Pd/Al 2 O 3 catalysts, isolated Pd active sites dispersed on the surface of the Al 2 O 3 support as egg-shell catalysts exhibited high activity for acetylene removal, which also inhibited the over-hydrogenation of ethylene to ethane. Therefore, it is significant to decrease Pd active site ensembles [5,7,11,16]. Figure 2a shows that the PdNPs on the PdNPs/α-Al 2 O 3 catalyst were smaller particles than those on the Pd/α-Al 2 O 3 catalyst ( Figure 2b).…”

“…For the selective hydrogenation of acetylene, supported Pd catalysts are used for the catalytic removal process. Therefore, supported Pd catalysts with low Pd loading still have attracted much attention in recent years [4][5][6][7][8][9][10]. The recent advance on supported Pd catalysts is to increase their ethylene selectivity and enhance their long-term stability.…”

Supported Cu Nanoparticles as Selective and Stable Catalysts for the Gas Phase Hydrogenation of 1,3-Butadiene in Alkene-Rich Feeds

“…12 − 18 Pd has a very high hydrogenation activity, which can result in a poor selectivity at high alkyne/alkadiene conversion in particular when large Pd assemblies are present. Therefore, the metal is often diluted or partially deactivated with appropriate modifiers (e.g., PdAg/Al 2 O 3 , PdS/CaCO 3 , and PdPb/CaCO 3 12 , 13 , 15 ). However, restructuring and metal segregation (e.g., when a large excess of diluting metal is present 19 or after oxidative regeneration of the catalyst 20 ) can lead to unwanted reactions such as isomerization, polymerization, and over-hydrogenation of the alkenes to alkanes which often results in limited selectivity and decreased catalyst lifetime.…”

“…Examples include the hydrogenation of polyunsaturated hydrocarbons to olefins, hardening of vegetable oils, and selective hydrogenation of various organic compounds such as vitamin intermediates , as well as pharmaceutical and agrochemical active ingredients. , The selective removal of polyunsaturated hydrocarbons from monounsaturated hydrocarbons is essential for the production of polymer- and synthesis-grade alkenes. ,− Polyunsaturated hydrocarbons, which are often present in crude alkene streams (e.g., 1,3-butadiene, up to 1–5 wt % in C 2 –C 4 steam cracking mixtures), interfere with the subsequent conversion of alkenes as they can degrade polymer quality and/or poison the polymerization catalyst. , Consequently, their concentration should be reduced to below tens of ppm. ,, This challenge is commonly addressed by selective hydrogenation of the residual polyolefins to the corresponding mono-olefins, commonly using palladium-based catalysts. − Pd has a very high hydrogenation activity, which can result in a poor selectivity at high alkyne/alkadiene conversion in particular when large Pd assemblies are present. Therefore, the metal is often diluted or partially deactivated with appropriate modifiers (e.g., PdAg/Al 2 O 3 , PdS/CaCO 3 , and PdPb/CaCO 3 ,, ). However, restructuring and metal segregation (e.g., when a large excess of diluting metal is present or after oxidative regeneration of the catalyst) can lead to unwanted reactions such as isomerization, polymerization, and over-hydrogenation of the alkenes to alkanes which often results in limited selectivity and decreased catalyst lifetime. , …”

Supported Ni–Au Colloid Precursors for Active, Selective, and Stable Alkyne Partial Hydrogenation Catalysts

“…Palladium and nickel are active hydrogenation catalysts that have long been used by industry for alkyne partial (or semi) hydrogenation. ,, However, both metals have low intrinsic alkene selectivity, as they overhydrogenate ethylene to ethane at low temperatures (<50 °C). In addition, Ni is a particularly active oligomerization catalyst and generates oligomeric side products (“green oil”) that deactivate the catalyst. − Various groups improved alkene selectivity using low Pd loading or Pd single sites. , Pd is also incorporated into PdM bimetallic catalysts to control catalyst selectivity and improve stability. Recent studies using PdZn alloys showed weaker alkene binding contributed to improved selectivity. , Both alkene selectivity and catalyst stability were further improved by preparing highly dilute Pd sites in Ga, Cu, − Au, − and Ag. , Of these, PdAg/Al 2 O 3 is widely used for industrial partial alkyne hydrogenation. , …”