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Catalytic activity of sulfated zirconia was affected by both sulfur loading level and surface crystal phase. Incorporating silica or alumina into the catalyst system stabilized the tetragonal crystal phase and prolonged activity. Stabilized sulfated zirconia prepared with 20 wt.% alumina maintained catalytic activity for the isoparaffin alkylation reaction six times longer than pure sulfated zirconia. This performance enhancement has, thus far, not been disclosed in the literature. Reasons for the enhanced performance are hypothesized. UV–Raman spectroscopy was used to characterize the surface structure of sulfated zirconia. Samples displaying tetragonal reflections were catalytically active, while those displaying a surface monoclinic phase showed little activity. Examination of fresh, spent, and regenerated catalyst did not reveal any evidence for a phase transformation, indicating catalyst deactivation was most likely caused by the accumulation of hydrocarbon fragments on the surface.

Infrared spectra of pyridine adsorbed on zirconia and Pt–zirconia exhibited bands consistent with Lewis acid sites. Sulfated zirconia, after heating at 400°C, exhibited bands indicating about equal amounts of Lewis (L) and Bronsted (B) acid sites; the B/L ratio decreased with increasing reactivation temperature to become essentially zero after reactivation at 600°C. In contrast, both Pt and Fe/Mn promoted sulfated zirconia exhibited B/L ratios that increased slightly with increasing reactivation temperature. It is proposed that pyridine reacts with a Lewis acid site to produce an adsorbed “pyridone-type” surface species with the concurrent generation of a proton. The superior performance of the promoted sulfated zirconia catalyst is believed to arise from its ability to generate Bronsted acid sites.

The formation of nitrogen oxides (NOx) during the regeneration of fluid catalytic cracking (FCC) catalyst can be attributed to oxidation of nitrogen in coke. Thermal NOx does not occur to any significant extent at FCC regenerator temperature. NOx is primarily comprised of nitric oxide (NO) with only a small concentration of NO2 detected. Under typical FCC regenerator conditions, only 10% of the nitrogen in coke evolves from the regenerator as nitric oxide with flue gases. Our findings show that ∼90% of nitrogen in coke is converted to dinitrogen (N2) in the regenerator. The authors suggest that dinitrogen is a secondary product produced by the reduction of NO with carbon and/or carbon monoxide in the regenerator. NOx emissions are lower in controlled burn regenerators where exposure to excess oxygen is minimized. Two-stage regeneration was found to lower NOx emissions by conversion to N2 during recontacting of flue gases and catalyst in the dense bed.

A method of interconversion of dry sieve and laser light scattering particle size values has been developed for cracking catalysts. Values obtained by light scattering techniques were consistently larger than those obtained by dry sieve analysis. The differences were primarily due to lack of sphericity of the particles. The particle size distribution determined by light scattering techniques was based on an average particle diameter. Conversely, the sieve measured the smallest diameter of the particle which can pass through the opening. Microscopic examination of commercial cracking catalysts confirmed their nonuniformity. The sphericity of the catalyst particles decreased as particle size increased. Therefore, the divergence between the laser light scattering and dry sieving value became greater as the catalyst particle size increased.

An investigation of the factors which affect the ratio of combustion products in the flue gas from a catalytic cracking unit has been conducted. Units which process resids have been found to suffer feed throughput penalties as a result of high CO2 2 /CO ratios. This study describes the effect of contaminant metals (nickel, vanadium and iron) on the combustion of carbon in the regenerator. Effects of these metals were investigated since they are deposited on the catalyst during the catalytic cracking process. Typical zeolite cracking catalysts were used in this study. The metal activity for the production of carbon dioxide increases from iron nickel. Results of this investigation show that nickel catalyzes carbon directly to carbon dioxide. Therefore, the amount of active nickel should be minimized to prevent high CO 2 /CO ratios in the regenerator. In addition, the active catalytic species can be effectively passivated by antimony when nickel and antimony are allowed to interact under reducing conditions.

Catalytic reforming technologies and processes have been the subject of numerous discussions and reviews over the past 50 years.[1-8] Since the pioneering work of Vladimir Haensel and UOP[9] on platinum on alumina catalyst and platforming in the 1940s, catalytic reforming technology has evolved from semiregenerative, fixed-bed processes to the more energy efficient, highly reliable, low operating cost, continuous catalyst reforming units.[10] Typical process objectives are the upgrading of low octane naphthas to high octane gasoline blending components, production of aromatics and chemical feedstock, and production of hydrogen. Over the past five decades, numerous advancements have been made with respect to key reforming processes and in the development of high-performance catalysts. In the current environment of low-sulfur gasoline and ultralow-sulfur diesel regulations for reducing air pollutants,[11] catalytic reformers and in particular, continuous reformers have become indispensable as support to refiners’ plans for installation of enhanced processes for hydrotreating catalytic cracker feed, distillates, and catalytic cracker gasoline. Refiners will be relying on their catalytic reformers for reliable hydrogen supply for the various desulfurization processes required to achieve near-zero-sulfur gasoline and ultralow-sulfur diesel.

Publisher Summary The metals passivation is the process of mitigating the deleterious effects of contaminant metals, thereby improving the catalyst activity and/or selectivity to more desired products. Metals passivation is accomplished today in two ways: (1) metering the metals passivation agent, usually via the fresh feed, into the cracker where it deposits on the catalyst or (2) incorporating additives during manufacture into the catalyst formulation or into a separate carrier particle, which is blended with the catalyst. Passivation additives are normally referred to as “metal traps.” In the case of passivation of vanadium, the average life of the cracking catalyst particle is prolonged. With nickel, passivation decreases dehydrogenation activity. The refiner usually has several ways to utilize the benefits of reduced yields of hydrogen and coke achieved through metals passivation. One economically attractive option for many refiners has been to crack resid blended with the traditional gas oil feed.